As Joe said, the error messages tell the deal … the file is corrupt/damaged … if you’re 110% sure it was originally rendered both properly and completely, it probably became corrupted/damaged while transferring from one drive to another or something similar.
The first thing I’d do is double and triple check my QuickTime … make sure you have the latest version and that it works fine with any other MOVs. You might also try opening the file on different computers … perhaps with an older version of QuickTime.
Also as Joe suggests, if you can get the file to open anywhere, run with it … in other words, see if you can get any conversion software to read it and export it to a new file (i.e., Squeeze, ProCoder, Cleaner, MPEG Streamclip, etc.).
This may seem overstating the obvious, but in my opinion, this can never be overstated … personally, I absolutely never have only one copy of any of my work (including all sources & project files). And, the 3-4 copies I keep are always in different places (i.e., external drives, backups, etc.) … computers are not infallible.
As an extra safeguard against this kind of thing, its also helpful to always embed project files into your QT movies … if you did that, try importing it as a project instead of as a MOV. Then, if you still have the source media, it’ll probably be much faster to re-render it than trying to get this file to work.