Outlook.exe crashing on ntdll.dll

Windows XP, MCE, SP 2.
Outlook 2003 Professional, SP2

About one time per day, Outlook crashes with the following in the Application Log:

Event Type: Error
Event Source: Microsoft Office 11
Event Category: None
Event ID: 1000
Date: 5/2/2006
Time: 2:07:03 PM
User: N/A
Computer:
Description:
Faulting application outlook.exe, version 11.0.8010.0, stamp 43d16d53, faulting module ntdll.dll, version 5.1.2600.2180, stamp 411096b4, debug? 0, fault address 0x00011f6e.

I do not see any patterns of errors or messages around these. Any advice would be appreciated!