Thanks for your speedy reply Shaun.
Yes, I think it must have been a Pinnacle… I really have posted in the wrong area, sorry!
Mpeg Streamclip didn’t work, but I’ll try ffmpeg now
I’ve managed to find a few other forum posts around the net from people with the same Pinnacle TARGA problem, and all of the these posters have eventually given up! Things are looking pretty bleak, but fingers crossed!
Thanks again for your help.