Bad news: that level file is 1.3 megabytes of air!
Something caused every byte in that file to become null. Not sure what to suspect. If Ved or VVVVVV were to have a file saving bug this catastrophic in a certain condition, if anything it'd save a file 0 bytes long, not a file filled with NUL bytes. If it were your harddisk, and this would have been a first sign of trouble 2.5 months ago, then I think it'd be a bit strange if nothing happened ever since (unless you didn't use the computer). But I'm not an expert on hard drives. Other than that, I can only conjure theories whatever caused it (some obscure OS bug? Malware? Power loss while saving?)
Do you know if this happened to any other files?