Sorry Gents, bit of a red herring.
I hadn't actually tried to add a SIP user as i had the error on the SIP DEVICES page.
However, after posting i thought maybe i ought to try it, and guess what . . . . .it worked
I still have the error, but i can connect SIP devices through the MBG to the controller and they work fine. Not sure what the error is all about but doesn't seem to be affecting the operation.
Currently running MBG 6.0
Thanks for the input and sorry for wasting your time.