DUPLICATE MEETING ENTRIES IN OUTLOOK

We use Outlook’97 clients and both Win95/98.
In the calendar part of Outlook we setup meeting appointments and invite internal staff to them which works great.

On one particular PC though when you setup the meeting, invite others and then send it, it inserts 2 duplicate meeting appts into the users calendar.
All the other clients are fine and when they setup a new meeting appointment just get the normal one entry into their calendar.
We use Exchange 5.5 at the back end.
Any reason why this one PC is different, is there an option somewhere?!