Help with QuickTime PLEASE!!!!!

I've been working on a home movie in Quicktime Player. It's about a 1Gb .mov file. But today I opened it, and I got a message saying that QuickTime could not open the movie, that it was "not a file that QuickTime understands" (-2048). How is it all of a sudden not a file QuickTime understands? I CREATED IT IN QUICKTIME!!!!!!!!!! Please tell me how do I fix this????

Thanks