When adding a shared calendar in outlook for MAC i get sync errors on an event which will not go and keeps adding.

It only appears to show in outlook for MAC and the permissions are set to reviewer? 

The error is: permission error, changes to the event " could not be saved because you do not have the appropriate permissions "

I have tried to clear the cache on the device and still appears, i have even cancelled the event in the calendar and it still brings up the error

Any help would be greatly appreciated?