I recently could not sleep and decided to do some coding (anyone else do that?) and deep in the bowels of my program came up with this gem:

seek(FOOBAR, 2, 0);
[download]

This appeared right before I was to write information (e.g. append) to the end of a file. Needless to say, the error was discovered very quickly! Luckily, I had a backup of the file in question. :)