Just to completeness - the issue solved. In the end I deleted the instance file on the OS and recreated adding back each of the performance parameters in groups of ones and two's - checking at each stage the problem didn't reoccur. I can't pin point a particular parameter that caused the problem as in the end the parameters all went back in as is. I then re-adjusted the EM parameters to look more sensible and reimported the profile back into RZ10.
Thanks for everyones help with this matter.
Liz