Accepted meeting requests not added to calendar

I have a user who can accept meeting requests, but the meetings are
not added
to his calendar.
When he receives a meeting request he accepts it, the message is
deleted & a notification is sent to the
originator but the meeting is not added to his calendar.

User is using outlook 2003, it's online and syncronised with the
exchange server.

Outlook is on-line and synched with the Exchange server.

I've checked that the delivery location is set to the users mailbox &
not a personal folder.
and i've also started outlook with the /cleanfreebusy switch.

Any suggestions?