When multiple people are working with CVS, what can sometimes happen when you do a “cvs update” is that binary files get “merged” as if they were text files. Naturally, this can cause some file types to become corrupt.
To avoid this happening, type:
$ cvs admin -kb path/to/binary.file
Usually, you have a large number of these files (in my case, I had about ~1000 zip files). So combining the above with Bash’s find can be very useful. Assuming you are in the working directory:
$ find . -name "*.ext" -exec cvs admin -kb {} ;
The “{}” substitutes the found file, which CVS marks as binary for you.
There is also a handy guide on working with binary files in CVS.