Outlook 2007 gets hung.

Hello,
We have a small office with 5 users, all using Office & Outlook 2007 on Win7 PCs. At various times, we all seem to encounter the same problem with Outlook - No new emails are received and the mail send stays in the Outbox. Selecting F9 just stacks up the Tasks. The Send/Receive Progress window displays 0 of XX Tasks have bee completed.

Exiting Outlook and restarting doesn't solve the problem, as some component/process continues to run (outlook.exe). Accessing the Task Manager and stopping the process clears Outlook and upon restart, new mail begins arriving and composed mail is sent.

I can find no common action that causes this. Some PCs experience the problem while others work as normal. The problem is not consistent on any 1 PC.

I have reviewed Microsoft forums which want to place the blame on the Mail Server. Other forums point to account setting, but nothing in this area is outside the required or norm. And all the PC Outlook apps work correctly most of the time. I can't find anyone who can point me in a valid direction or verify that Outlook is just flaky.