I recently had a problem with users' mailboxes hanging when the users tried to view their Outlook Calendar. Apparently, conference rooms that use AutoAccept scripts to accept meetings can corrupt certain Calendar items (i.e., recurring appointments) because the scripts can incorrectly modify First Day of the Week data. The solution that Microsoft offers is to download and apply the most recent version of cdo.dll, which is available as part of an Exchange Server 5.5 postService Pack 4 (SP4) hotfix. The new cdo.dll keeps this problem from recurring but doesn't fix a Calendar that's already corrupted. (The Microsoft articles "XADM: CDO Can Corrupt Data in Recurring Appointments," at http://support.microsoft.com/default.aspx?scid=kb;en-us;q281935, and "XGEN: Exchange Server 5.5 Post-Service Pack 4 Collaboration Data Objects Fixes Available," at http://support.microsoft.com/default.aspx?scid=kb;en-us;q289606, discuss this problem and its prevention.)
After trying to be a detective and wasting hours looking for a way to fix a corrupted Calendar, I finally asked for advice from the Exchange community and found out about scancal.exe, a tool available only from Microsoft Product Support Services (PSS). I called PSS to request the tool, and within minutes, I was able to find the corrupt recurring appointments in the mailboxes that were hanging. I then used Outlook Web Access (OWA) to access the mailboxes and delete the corrupted items.