Echange 2000 and Outlook 2000+

Having extremely annoying issue here. Upgraded from Exchange 5.5 to 2000 in January and all was smooth for awhile.

Now, it seems like a lot of my users (including myself) are having issues with Outlook locking up and a window popping up saying that it is trying to retrieve info from the exchange server. This is beginning to become a major issue and I need to find a fix soon, but can not find any info on MS.com. Talked with a peer and he said he was having the same issue with Outlook XP and had no fix.

Any comment or help?

Thanks,
Stephen