Thank you for the response, unfortunateley I allways have my Object Info palette (and other pallets) free floating as it gives me more screen space.
So based on your advice I did the reverse and attached it! It seems to have fixed it on the iMac 27" (Late 2015).
However, not on the iMacPro 27" (2017)! I have even tried to put it back and take it off again - still the same result of having to Force Quit!
It was all rather embarassing today when it crashed whilst trying to create a revised elevation for a client.
Do you know when will SP3 be coming out?