State Management :: Authentication Cookie Expiration Not Sliding Properly?

we have a web based application that let users register, activate their account and then login to use the app...

it is very important that accounts must not be used simultaneously, so if user a is logged in using mynameisA/mypassword, no one else can login at the same time using the same credentials, until he logout.

this was achieved by using a cache mechanism that inserts an entry specific to that user and will keep on refreshing at each request, until the user logouts, where we remove that cache entry. on login, we check whether that cache entry is there in order to allow him in or throw a message saying that the user is already logged in... we use enterprise library 5.0 which we found more reliable than the asp.net cache, and for various other practical reasons.

now, this works fine, but the problem is that it seems like the authentication ticket and cookie doesnt slide properly at each request. so sometimes, users end up logged out because their authentication ticket got expired, and they cannot login again because the cache entry is still there.

here is the code in the sign-in page:

' if user credentials are valid, and other checks and validations...

[Code]....

here is the code that runs on every authenticated request (httpmodule):

[Code]....

and here is the web.config stuff:

[Code]....

we've done all kind of tests including metabase IIS6 monitoring. there is no apppool recycle happening...

checking the authentication cookie in firefox view cookies option shows that on each request, the expiration time of the authentication cookie is not sliding.