<div>
Of course this is no substitute for building error handling into your code. :) <br />
<br />
In addition to the links provided by rachitkohli, which show examples of trapping and logging the error. I like to add a few additional details to help diagnose the situation. The email notification that I receive when an unhandled exception occurs includes not only the usual exception info (message, stack trace, etc), but I also include httpcontext info... <br />
<br />
Request.ServerVariables(&quot;A<wbr />LL_HTTP&quot;)<br />
Request.ServerVariables(&quot;R<wbr />EMOTE_ADDR<wbr />&quot;)<br />
Request.ServerVariables(&quot;A<wbr />UTH_USER&quot;)<wbr /><br />
Request.ServerVariables(&quot;S<wbr />CRIPT_NAME<wbr />&quot;)<br />
<br />
Depending on your situation you may not need these, or you may wish to included different server variables.<br />
<br />
Hope this helps.
</div>


<div>
You may want to use the global.asax file. Just add any code you want to handle the error there. You'll have full access to session and server variables in this event through System.Web.HttpContext.Cur<wbr />rent.<br />
<br />
protected void Application_Error(Object sender, EventArgs e)<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//Do what you want with error here...<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Response.Redirect(&quot;error.a<wbr />spx&quot;);<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />
<br />

</div>


<div>
i see a lot of helpful stuff but nothing helped me with this error<br />
<br />
ERROR<br />
A potentially dangerous Request.Form value was detected from the client (CWIDT=&quot;&quot;). <br />

</div>


<div>
That error is a security precaution. You'll get it if you try to submit text with what looks like html code.<br />
<br />
If you want your users to be able to enter html code, try adding validateRequest=&quot;false&quot; into the Page-directive on top of the page.<br />
<br />
You could also add it to your web.config file, but I would advise against it as it will affect all pages on your site.
</div>


<div>
i want to prevent the user from puting HTML code in the text 
</div>


<div>
In that case, you'll have to do some server-side validation. see here for example:<br />
<br />
<a href="http://msdn.microsoft.com/en-us/library/bb355989.aspx" rel="ugc">http://msdn.microsoft.com/en-us/library/bb355989.aspx</a><br />
<br />
<br />

</div>


<div>
i dont understand that site that much i have used validators and it did not work can you show me an exmaple of what i can do to prevent this error from happening
</div>


<div>
what will this validate <br />
<br />
ValidationExpression=&quot;^[a-<wbr />zA-Z'.\s]{<wbr />1,40}$&quot; 
</div>


<div>
It limits the txtName field to alphabetic characters (lowercase and uppercase), space characters, the single apostrophe for names such as O'Dell, and the period. In addition, the field length is constrained to 40 characters.<br />
<br />
On postback, if the txtName field does not meet the validation criteria, the ErrorMessage is displayed.
</div>


<div>
&gt;&gt;&gt;i see a lot of helpful stuff but nothing helped me with this error<br />
<br />
&gt;&gt;&gt;ERROR<br />
&gt;&gt;&gt;A potentially dangerous Request.Form value was detected from the client (CWIDT=&quot;&quot;). <br />
<br />
Are you sure strickdd's comment on using Application_Error in Global.asax is not catching this error? I believe it will catch this type of error. <br />
<br />
As far as how to prevent/handle this error, it is another question.<br />
<br />
By default, you cannot use try/catch block in code behind to catch this error because the framework will catch that error before it gets to your code. That it why you will need to use Global.asax to catch it if you need to. However, if you set validateRequest=false (either on a specific page directive, or for the whole application through web.config), you are telling the framework to let the request go through without any sanitization, and you will do the clean-up yourself before saving the data to the database.<br />
<br />
Regular expression or JavaScript can be used to prevent user from entering HTML tags on the client side, but you will still need to sanitize the input at the server side because it is easy to bypass the client side validation. You may use HtmlEncode to encode the text input before you save it to the database.<br />
<br />
Here is a simple and quick example that will prevent usere from entering any URL in the text box:<br />
<br />
&lt;script language='JavaScript' type='text/javascript'&gt;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;function checkUrl(){<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;var theUrl;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;var theBox;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;var theButton;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theUrl = document.getElementById('i<wbr />nputTxt');<wbr /><br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theButton = document.getElementById('s<wbr />ubmitBtn')<wbr />;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if(theUrl.value.indexOf('<a href="http://) >= 0 || theUrl.value.indexOf(" rel="ugc nofollow">= 0 ||<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theUrl.value.indexOf('http<wbr />s://') &gt;=0 || theUrl.value.indexOf('www.<wbr />') &gt;=0){<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theButton.disabled = true;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} else {<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;theButton.disabled = false;<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />
&lt;/script&gt;<br />
<br />
Then you attach this JavaScript function to the &quot;onchange&quot; event of your text box. What it does is if user enters a URL in the textbox, it will disable the submit button so the user will not able to submit the form until the URL is removed.<br />
<br />
Like I said, it is just a quick and dirty example to get you started. There are a lot of rooms for improvement in the code.</a>
</div>


<div>
The error you described occurs when a form field has an HTML character in it (i.e. &quot;&lt;&quot;). <br />
For that error, you just need to add to following into your &lt;@Page&gt; tage:<br />
<br />
&nbsp;ValidateRequest=&quot;false&quot;<br />
<br />
This is not the best idea in all cases though. You may want to have a javascript function that will HTMLEncode all your form field when they click submit.
</div>


<div>
ok can simeone put a example up using vb
</div>


<div>
Same example as above in VB:<br />
<br />
&lt;%@ Page Language=&quot;VB&quot; ValidateRequest=&quot;false&quot; %&gt;<br />
<br />
&lt;script runat=&quot;server&quot;&gt;<br />
&nbsp; &nbsp; Sub submitBtn_click(ByVal sender As Object, ByVal e As EventArgs)<br />
&nbsp; &nbsp; &nbsp; &nbsp; response.Write(httputility<wbr />.HtmlEncod<wbr />e(inputTxt<wbr />.Text))<br />
&nbsp; &nbsp; End Sub<br />
&lt;/script&gt;<br />
<br />
&lt;html &nbsp;&gt;<br />
&nbsp; &lt;body&gt;<br />
&nbsp; &nbsp; &lt;form id=&quot;form1&quot; runat=&quot;server&quot;&gt;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &lt;asp:TextBox ID=&quot;inputTxt&quot; Runat=&quot;server&quot;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;TextMode=&quot;MultiLine&quot; Width=&quot;382px&quot; Height=&quot;152px&quot;&gt;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &lt;/asp:TextBox&gt;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &lt;asp:Button ID=&quot;submitBtn&quot; Runat=&quot;server&quot; Text=&quot;Submit&quot;<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; OnClick=&quot;submitBtn_Click&quot; /&gt;<br />
&nbsp; &nbsp; &lt;/form&gt;<br />
&nbsp; &lt;/body&gt;<br />
&lt;/html&gt;
</div>


<div>
so what does this do <br />
<br />
response.Write(httputility<wbr />.HtmlEncod<wbr />e(inputTxt<wbr />.Text))
</div>


<div>
HTML encoding converts characters that are not allowed in HTML into character-entity equivalents. For example, when embedded in a block of text, the characters &lt;&nbsp;and &gt;&nbsp;are encoded as &lt;&nbsp;and &gt;&nbsp;<br />
<br />
If you run the example code, it will write back to the page an html encoded string of the value of the inputTxt textbox. You will have to view the source of the page to see what it actually does. <br />
<br />
Enter &nbsp; &lt;b&gt;test&lt;/b&gt; &nbsp; &nbsp;into the box and click Submit. The text at the top of the page will read: &lt;b&gt;test&lt;/b&gt; but if you view the source, you will see that it is actually converted to: &nbsp; &lt;b&gt;test&lt;/b&gt;<br />

</div>


<div>
Acutally, &nbsp; &amp;amp;lt;b&amp;amp;gt;test&amp;amp;<wbr />lt;/b&amp;amp;<wbr />gt;<br />
<br />

</div>


<div>
ok i tried to debug it so i can see ahat this does,but i still get that same error if i enter any type of html code in it.HTML code is bad so what all do i need to add<br />

<pre><code class="code-10 nolinks" id="code-127528"><span>           Response.Write(HttpUtility.HtmlEncode(CWID.Text))</span>
<span>            If CWIDT.Text = UIN Then</span>
<span>                Session(&quot;CWID&quot;) = Me.CWIDT.Text.Trim</span>
<span>                fname = DBGetField(rs, &quot;FIRSTNAME&quot;)</span>
<span>                lname = DBGetField(rs, &quot;LASTNAME&quot;)</span>
<span>                Session(&quot;FIRSTNAME&quot;) = fname</span>
<span>                Session(&quot;LASTNAME&quot;) = lname</span>
<span>                Response.Redirect(&quot;auth.aspx&quot;)</span>
<span>            Else</span>
<span>                rs.MoveNext()</span>
<span>                msg.Text = &quot;UIN is incorrect&quot;</span>
<span>            End If</span>
</code></pre>
</div>


<div>
In this situation, I would validate the CWIDT control using the regex validation control mentioned above. If the validation fails (i.e. html code is entered in the textbox), the page will not continue.<br />
<br />
<br />

<pre><code class="code-1 nolinks" id="code-127536"><span>&lt;asp:RegularExpressionValidator id=&quot;nameRegex&quot; runat=&quot;server&quot;</span>
<span>        ControlToValidate=&quot;CWIDT&quot;</span>
<span>        ValidationExpression=&quot;^[a-zA-Z'.\s]{1,40}$&quot;</span>
<span>        ErrorMessage=&quot;Incorrect format&quot;&gt;</span>
<span>  &lt;/asp:regularexpressionvalidator&gt;</span>
</code></pre>
</div>


<div>
the validator works great it will not let me enter anything i<br />
here rae things that i need to enter <br />
numbers up to 9 digiuts<br />
and the word admin
</div>


<div>
Someone more versed in regex can refine this further, but this code will accept any combination (up to 20 characters) of numbers 0-9 and letters a, d, i, m, n<br />
<br />
Anything other than that and the validation will fail. You could also use the MaxLength property of the textbox to restrict the amount of characters that can be entered.<br />

<pre><code class="code-1 nolinks" id="code-127573"><span>&lt;asp:TextBox id=&quot;CWIDT&quot; runat=&quot;server&quot;&gt;&lt;/asp:TextBox&gt;</span>
<span>  &lt;asp:RegularExpressionValidator id=&quot;nameRegex&quot; runat=&quot;server&quot;</span>
<span>        ControlToValidate=&quot;CWIDT&quot;</span>
<span>        ValidationExpression=&quot;^[adimn0-9\s]{1,20}$&quot;</span>
<span>        ErrorMessage=&quot;Invalid entry&quot;&gt;</span>
<span>  &lt;/asp:RegularExpressionValidator&gt;</span>
</code></pre>
</div>


<div>
ok this works thank you <br />
<br />
is there any more error handleing i can do to prevent anytype of errors
</div>


<div>
There are several things you can do to prevent/minimize some kinds of errors/exceptions. Here are just a few. Many more can be found with some web searches, but most can be found by trial &amp;&nbsp;error.<br />
<br />
1. Write error-free code<br />
2. Learn to identify statements that may throw exceptions, and handle them accordingly<br />
3. Anticipate and plan for potential system failures (internet connection failure, db not available, printer not working, etc.)<br />
3. Keep your data strongly typed in all systems<br />
4. Program on the defensive... or if a step can be validated, do it. For example instead of opening a file, prevent a potential exception and first check to see if the file exists.<br />

</div>


<div>
LOL ,i have done all these things to my knowlege &nbsp;but i was needing to know of new things i can do to prevent errors later in my application<br />
<br />
1. puting html code in a textbox<br />
2.looking at the file location in the address bar 
</div>


<div>
It's probably best to start a new question to cover the topics your asking about. I'll be glad to help, but don't want to veer off the question/solution of your original inquiry.
</div>


<div>
ok but i think i found a way to have a universal error handler i just dont know how to do it <br />
<br />
if any error that was unhandled &nbsp;happend then redirect to an error page
</div>


<div>
Correct. And there are some examples of how to do that in the first couple posts.
</div>


<div>
is this the code to do tat <br />

<pre><code class="code-1 nolinks" id="code-131404"><span>&lt;customErrors mode=&quot;On&quot; defaultRedirect=&quot;error.htm&quot;&gt;</span>
<span>    &lt;error statusCode=&quot;500&quot; redirect=&quot;error500.aspx?code=500&quot;/&gt;</span>
<span>    &lt;error statusCode=&quot;404&quot; redirect=&quot;filenotfound.aspx&quot;/&gt;</span>
<span>    &lt;error statusCode=&quot;403&quot; redirect=&quot;authorizationfailed.aspx&quot;/&gt;</span>
<span>&lt;/customErrors&gt; </span>
</code></pre>
</div>


<div>
Yes, when added to the web.config file, that is one way to handle application errors.
</div>


<div>
great answers not what i was &nbsp;looking for but good answers
</div>


<div>
<div class="content wysiwyg-content">
i need a type of universal error handler to say if there is an error on my form to redirect to a page to prevent runtime errors
</div>
</div>


i need a type of universal error handler to say if there is an error on my form to redirect to a page to prevent runtime errors

i need a good error handler

The .NET Framework is not specific to any one programming language; rather, it includes a library of functions that allows developers to rapidly build applications. Several supported languages include C#, VB.NET, C++ or ASP.NET.

.NET Programming

The successor to Active Server Pages, ASP.NET websites utilize the .NET framework to produce dynamic, data and content-driven web applications and services. ASP.NET code can be written using any .NET supported language. As of 2009, ASP.NET can also apply the Model-View-Controller (MVC) pattern to web applications