Is there a way to configure the timeout value of the __VIEWSTATE hidden variable

A developer found a work-around that allowed him to use the __VIEWSTATE parameter to pass login information from their domain to ours and then bypass our login.  See code below:

 <form name="_ctl0" method="post" target="_blank"

   <input type="hidden" name="__VIEWSTATE"
g==" />

   <input type="hidden" name="txtUsername" value="<%=username%>"
id="txtUsername" />
   <input type="hidden" name="txtPassword" value="<%=password%>"
id="txtPassword" />
   <input class="btn" onmouseover="this.className='btnhov'"
onmouseout="this.className='btn'" type="submit" name="_ctl3" value="View Usage Reports" />
   <!--<a href="#" onClick="document._ctl0.submit()">Login to see Report</a><br><br>-->

The above workaround would work for approximately a month at which point the _VIEWSTATE value would need to be updated.  But when we upgraded from Windows 2000/IIS5 to Win2003/IIS6 the developer is now having to change the value daily.

We are trying to find the easiest way to accomodate this requirement without any code changes to our site.  Is there a way we can increase the life of the __VIEWSTATE variable?  

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As far as I can tell, ViewState is a page variable that has no relation to session timeout.  You can write code which attaches ViewState to the Session State, and change your ASPX pages to get ViewState from the session.

There are occasions in IIS6 when the saved ViewState on the server will go away -- when the application pool is refreshed.  That might be what you're seeing.  See this article from Microsoft on possible causes of invalid ViewState (you don't give the error that your developer sees, so I can't tell if this is the case for you):

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