The four registry mods are:
The above need to be added to allow the join to work. Then find the key below and set those values to 0.
This is definitely reported to work on many occasions across the 'net but doesn't for me. I may be being jinxed by having done an in-place upgrade and although I have a spare machine to try an install with, I haven't yet found the time.
Note that it is reported that you still get an error about the DNS suffix after these mods but the connection works - there is some Samba chatter about DNS suffixes but I only half understood it and since I haven't got that far yet, I didn't apply myself to it