What type of device are you using? How large is your Exchange calendar currently with approximately how many items?
In case the issue is simply a corrupted item in your calendar, you might have luck by clearing out your calendar from your Exchange mailbox. Be sure to export your Exchange calendar to PST file via Outlook first so that it can be restored later. Configure Activesync on your device while the calendar is empty and import your calendar back using Outlook when (and if) everything is working properly. Before importing you may want to try issuing a PST repair on your exported PST file, see
http://office.microsoft.com/en-ca/ou...563001033.aspx for details.