Thanks for your response.
All images were Jpegs
One more thing,
Now I am unable to open any folder in Capture One
Okay, for version, I meant which is running, 5 Pro, 5 basic, or DB? I am on Mac, but I think on the Win version you only get a "Proof" capability for jpegs, not any processing -- not 100% sure here though. What happens with a raw file?
When you say "open a folder" are you importing the images into a C1 sessions folder first, or trying to open an existing folder of images before importing them into a session?
So try actually importing a few raw files from your 40D's card to a session folder and see what happens...