Problem importing video

Argh – issues. I am working on a score using C5 (5.5.2) and lo and behold I look up and all of a sudden my video track (with thumbnails) has disappeared… when I look in the Pool, it says “Invalid or unsupported file.” Which is funny, because it was working just fine for hours. However, when I try to re-import the video (which is MPEG4), the GUI gives me the same error. There’s nothing wrong with the video file itself, it plays back fine outside Cubase. I do have the latest version of QuickTime (v 7-something). I have a suspicion this is due to a corrupted .cpr file, because if I start a whole new project from scratch, and then try to import the video, I don’t get any error, it imports fine. If I have to I will follow that course of action, but I was hoping someone had an idea for a simpler fix. I suppose I should just upgrade to C8 :laughing:

System:

Win 7 64-bit
Cubase 5
8 GB RAM