Sorry for the double-post, but also you can check if your file is corrupt by checking the checksums. You can use a plug-in called HashCheck on a Windows computer - or search google for linux/mac programs. That will save you downloading the whole file again if you don't need to. It doesn't matter if the file is renamed the checksums will remain the same (but they will change if you re-mux it in the new file as per my previous post).
A torrent automatically checks the hashes of the pieces to ensure you don't get a corrupt file.
Here are the checksums using hashcheck:
