Calendar printing error

I have two desktops, both XP Pro / Office 2003, all service packs / fully
patched, one used by our CEO and another by his Admin Assistant. Outlook is
configured to connect to an Exchange 2003 server for calendaring functions.
The admin assistant has full rights on the CEO's calendar and can view it,
edit it, etc without difficulty. However, she cannot print the CEO's calendar
from her desktop. When she tries to print or print preview the CEO's
calendar the following message is displayed:

The messaging interface has returned an unknown error. If the problem
persists try restarting Outlook.

I have removed / re-installed Office, applied all up-to-date patches, etc.
There are no errors in the Event Logs that relate and I have found nothing in
the Knowledge Base to suggest possible causes.

I appreciate any assistance, ideas, etc

Thanks,

Don