What could be the problem with my Calendar?

I have an HTC Incredible mobile phone which I synchronized with my Outlook through Microsoft Exchange/Active Sync. I seemed to have succeeded because information on my Calendar is appearing on my device. After a few days, these information are not showing up on my Calendar anymore. If I enter new information on Outlook, these do not show up as well. I am still able to access my email and contacts without difficulty whether these are entered using Outlook or through synching with my HTC Incredible.
What could be the problem with my Calendar?
Thanks for your help.
