ASP.NET Membership Issue

I've searched all over the place for this issue, and I haven't had any luck.  Hopefully some here can help me.   I'm currently hosting a website on a shared hosting server.  My website uses asp.net 2.0 membership and I have session state mode set to "InProc".  I have an intermittent issue where users log into the website, and it appears they are authenticated, but everytime they try to go to another page (or perform a postback) they get redirected to login again.  This doesn't happen all of the time, but it seems like when it does it happens to users who don't check the "remember me" option.   Does anyone have any ideas on what would cause this behavior?  Have you seen this before?  I have included my login code, Session_Start, Session_End and my sessionState config entry.   Thanks in advance.     Login Code ...