Rob, thanks for the help earlier.
Took the VEMS to a friends for the evening, connected it up to his car battery and my laptop, problem persisted, changed over to his laptop and both the firmware and temp files uploaded immediatley!
I've now got his laptop on loan incase I need to change other files etc.... it's too late now to connect back upto my car to check correct figures, but fingers crossed, having VEMS able to connect to megatune again is a great relief.
Cheers
Alex