I'm having reports and complaints from my user that they will be using a screen and get kicked back to the login screen immediately on their next request. It doesn't happen all the time but randomly. After looking at the Web server the error that shows up in the application event log is:

Event code: 4005 Event message: Forms authentication failed for the request. Reason: The ticket supplied has expired.

Everything that I read starts out with people asking about web gardens or load balancing. We are not using either of those. We're a single Windows 2003 (32-bit OS, 64-bit hardware) Server with IIS6. This is the only website on this server too.

This behavior does not generate any application exceptions or visible issues to the user. They just get booted back to the login screen and are forced to login. As you can imagine this is extremely annoying and counter-productive for our users.

Here's what I have set in my web.config for the application in the root:

<authentication mode="Forms">
      <forms name=".TcaNet"
        protection="All"
        timeout="40"
        loginUrl="~/Login.aspx"
        defaultUrl="~/MyHome.aspx"
        path="/"
        slidingExpiration="true"
        requireSSL="false" />
    </authentication>

I have also read that if you have some locations setup that no longer exist or are bogus you could have issues. My path attributes are all valid directories so that shouldn't be the problem:

<location path="js">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>
  <location path="images">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>
  <location path="anon">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>
  <location path="App_Themes">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>
  <location path="NonSSL">
    <system.web>
      <authorization>
        <allow users="*" />
      </authorization>
    </system.web>
  </location>

The only thing I'm not clear on is if my timeout value in the forms property for the auth ticket has to be the same as my session timeout value (defined in the app's configuration in IIS). I've read some things that say you should have the authentication timeout shorter (40) than the session timeout (45) to avoid possible complications. Either way we have users that get kicked to the login screen a minute or two after their last action. So the session definitely should not be expiring.

Update 2/23/09: I've since set the session timeout and authentication ticket timeout values to both be 45 and the problem still seems to be happening.

The only other web.config in the application is in 1 virtual directory that hosts Community Server. That web.config's authentication settings are as follows:

<authentication mode="Forms">
    		<forms name=".TcaNet" 
    		protection="All" 
    		timeout="40" 
    		loginUrl="~/Login.aspx" 
    		defaultUrl="~/MyHome.aspx" 
    		path="/" 
    		slidingExpiration="true" 
    		requireSSL="true" />
    	</authentication>

And while I don't believe it applies unless you're in a web garden, I have both of the machine key values set in both web.config files to be the same (removed for convenience):

<machineKey 
        validationKey="<MYVALIDATIONKEYHERE>" 
        decryptionKey="<MYDECRYPTIONKEYHERE>" 
        validation="SHA1" />

<machineKey 
    	validationKey="<MYVALIDATIONKEYHERE>" 
        decryptionKey="<MYDECRYPTIONKEYHERE>" 
    	validation="SHA1"/>

Any help with this would be greatly appreciated. This seems to be one of those problems that yields a ton of Google results, none of which seem to be fitting into my situation so far.