Hi Dave,
Thanks, I have now solved the issue.
Someone provided me with 7.51 FXT009 firmware.
At your suggestion I ran AT+WOPEN=4 to delete my OAT application first (I was already running AT+WOPEN=3) and I was able to go from 7.47.4 to 7.51. I xmodem downloaded w.dwl, then dwl.dwl and then finally the 7.51 FXT009 firmware.
I then upgraded OK from 7.51 to 7.52.
AT+WOPEN=4 may have been the command that fixed my problem or I may have needed the 7.51 upgrade step or I may have needed both.
Best Regards
Tom