Outlook client constantly loading the regarding section in appointments

Hi 

We have recently updated to service pack 1 roll up 3 for CRM 2013. We are completing some testing and the users are experiencing some strange behavior with appointments.

These sync without any issue but the regarding section goes into what looks like a loading state and continues circling forever with no end. 

Has anyone seen anything like this or even better has a solution. 

Thanks

Dan