innuendo, gas path and A-V-8R
Many thanks for those tips. I have managed to get both cards working again as 'film' cards by formating them in my Dimage 1500EX. The 1500 was able to do this even though the Dimage 7 couldn't.
It sounds as though the defrag/scandisk route would be useful so will go searching.
The dpreview.net forums are absolutely HUGE - most interesting.