I had the same problem, until I realised the file size for all of my templates was 0 bytes! No wonder it didn't recognise the file type, there wasn't even enough info there to pull up a blank page. I suggest either reinstall Illustrator from your CS disks or maybe copy the files over from the bonus disks you get with CS? (I know there's a load a templates there, it's just that I've never looked at them yet!