Just a follow up for those who helpfully posted in my hour of need.
After trying everything that was suggested and checking every setting and .dll I still had the problem of a single users calendar not syncing correctly.
I was in the process of documenting the log files for sending to RIM and Hey Presto all is fine!!!
So all I can think of is that my Blackberry server has become self aware and can repair itself. If only my users were the same!
Anyway, thanks to all who posted.