ASP.net Strange Error

Hi

In my ASP.net web app I am suddenly getting the following error.
I make the changes in web.config but this results in the error further down

Server Error in '/' Application.

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

 Exception Details: System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

Source Error:


 The source code that generated this unhandled exception can only be shown when compiled in debug mode. To enable this, please follow one of the below steps, then request the URL:

1. Add a "Debug=true" directive at the top of the file that generated the error. Example:

   <%@ Page Language="C#" Debug="true" %>

or:

2) Add the following section to the configuration file of your application:

<configuration>
    <system.web>
        <compilation debug="true"/>
    </system.web>
</configuration>

 Note that this second technique will cause all files within a given application to be compiled in debug mode. The first technique will cause only that particular file to be compiled in debug mode.

Important: Running applications in debug mode does incur a memory/performance overhead. You should make sure that an application has debugging disabled before deploying into production scenario.  



'++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Server Error in '/' Application.

Configuration Error
  Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

 Parser Error Message: Sections must only appear once per config file.  See the help topic <location> for exceptions.

Source Error:



Line 68:       </providers>
Line 69:     </roleManager>
Line 70:     <compilation debug="true"/>
Line 71:   </system.web>
Line 72:   <system.webServer>
 

 Source File:  C:\Users\murbro\Documents\Visual Studio 2010\Projects\Pivot\Pivot\web.config    Line:  70
Murray BrownMicrosoft Cloud Azure/Excel Solution DeveloperAsked:
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Pratima PharandeCommented:
could be that IIS recycled your app and therefore you get new keys for the session/view state. To alleviate this, add a machine static key in the web.config
Generate a key from http://www.eggheadcafe.com/articles/GenerateMachineKey/GenerateMachineKey.aspx

And place the keys in your web.config example as below

<machineKey
validationKey="56AB7132992003EE87F74AE4D9675D65EED8018D3528C0B8874905B51940DEAF6B85F1D922D19AB8F69781B2326A2F978A064708822FD8C54ED74CADF8592E17"
decryptionKey="A69D80B92A16DFE1698DFE86D4CED630FA56D7C1661C8D05744449889B88E8DC"
validation="SHA1" decryption="AES" />

refer for more details
stackoverflow.com/questions/6259844/asp-net-validation-of-viewstate-mac-failed
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Murray BrownMicrosoft Cloud Azure/Excel Solution DeveloperAuthor Commented:
Thanks for the help
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