I am not sure, but I think I have a similar problem.

A customer runs FB SS on a Windows 2003 Dual Core Server.
Sometimes (a few days after booting the server) FB slows down
dramatically. Processor usage goes up to 50%.
A restart of the FB service doesn't help. I have to restart the
Windows 2003 server, to solve the problem. This is very awkward,
because the customer works in 3 shifts and there is allways anyone
connected to the database.

What could be the reason for this problem? Are there any knowen issues
on this?
What could I try to solve this problem?

Kind regards
Helmut