Access db 2007 not responding problem

I am using office 2007 access db. I have develop db and install at
Server windows xp 2003 R2. Our client side is Windows Vista.
users access the 2007 db from client side to server folder.

access 2007 db working but when user want to access / run the report
it give message " Report (Not Responding) "

what is the problem of this error ?
why it give this error and not work ?

when as access 2007 form is working fine. some time, it work and some time
it give not responding message and not work why ?

I also update the windows vista and ms office 2007 service pack 1.
but problem is still the same.

Please help to solve above problem ?

Thanks and regards
Mateen