Outlook is freezing

I have a client that is having a problem with their outlook freezing. 4 of
the 5 users are using Outlook 2003 and the other user is using Outlook 2007.
All the users are connecting to a hosted exchange server 2007 using RPC over
HTTP. All 5 of the computers are freezing at various times of the day and in
other locations outside the office. The office has a DSL connection that
supports the 5 computers in the office with no other issues as far as
internet speed.

Do you have any thoughts on what could be causing Outlook to freeze on all 5
computers?

Thanks

Jim