Hello Ken - and, as always, many thanks for your reply.
Clearly I sent the wrong log, a probable result of not knowing exactly when the problem occured and not being able to read/understand the log contents. I re-visited the log folder to find that the logs had apparently been deleted ..... but not knowingly by me, so I cannot re-check them.
When this has happened before, the program freezes. Any key touched brings up the totally white screen. There is no option but to close the program down. I have the 'autosave sequence' option set but it never (seems to) save anything anyway. My only other option would be to anticipate the possibility of a crash and save the sequence every minute or so before running it.
FWIW the next day all ran fine but that had problems not related to SGP.
Yes, I now realise the other program may have used the native driver instead of ASCOM. I try to keep a standard configuration but I cannot be certain. I could easily do a test download as you suggest.