Shared calendar issue

In Exchange 2003 environment the client is running Office 2003. Customer has
access to a shared department calendar. She had edit rights. She can view the
calendar but any entries are not saved.

There was an issue with reminders which was resolved by the Exchange team.
I was told that the reminders needed to be synchronized.

I even granted this customer owner rights. She can see the calendar, attempt
to make entries but she cannot save any entries.

Incidentally she has access to other shared calendars with edit rights and
can save new entries. It would apprear it is something to do with this
mailbox.

Any ideas?