Login Failed/Mailbox is Unavailable Errors

Since updating to WebAcces 8.00.01 (9/27/2009), every so often WebAccess starts denying connections. Users receive a "Your mailbox is unavailable. Please contact your system administrator" message and see a bunch of "Login Failed" errors on the WA console screen.

I've looked at the log, verified I'm not hitting an MaxUsers or thread limit but don't see anything obvious. Once I restart GWINTER, everything is good for a few more days.

The really good news is that the 9/27/2009 GWINTER patch fixed the abending issue!

Any ideas on what might cause this or is it another GWINTER bug?