x.509 Certificate timeout problem

I have recently upgraded my client app to .NET 2.0 to take advantage of the 2.0 framework's enhanced certificate classes. The app polls a web service
for information. In the environment that we're in all sites must use certificate authentication. Users login to their PCs using CAC card device
which requires them to enter a PIN when they login. The issue is that if a user is idle the PC is set to lock their machine (not my app the OS times
out and automatically locks the machine). To unlock the machine the user has to re-enter their PIN. The problem is that my app then starts asking
them to re-enter their PIN on every poll attempt. I'm not sure why it does this. The only think I can think of is that the method that is used to
retrieve the certificate is a static method and somehow it's caching the PIN/certificate so during the initial login it was working fine but after teh
re-login it is using some old info. I can try to create the method as a non-static method but I'm wondering if the original caching that was taking
place will stop and now they'll have to enter the PIN all the time. I don't have one of these CAC card devices to test with so I have to do a little
guessing.

If anyone has any experience with this I'd sure appreciate some help as we've been given a very short deadline.