XP Pro SP3 security error

Hello I have an XP pro machine that I just updated to SP 3. It is a part of
domain A. I have a mapped network path to a 2003 server on domain B. After SP
3, nearly 100% of the time when our user clicks on a link to the server on
domain B, we get the error message: "The system detected a possible attempt
to compromise security. Please ensure that you can connect to the server that
authenticated you." I have to delete this mapped network path before I am
able to reconnect to the server. Once I've reconnected, the path works for a
time.

I have a second machine with the same senario above, but is still at SP2 and
never had such issues. Therefore, it seems to me to be a SP3 bug.

Does anyone know how we are supposed to keep SP3 happy? What is driving this
behavior? Is there some new and improved setting that I need to set, beyond
keeping AD happy? Thanks.