I got this when building a solution in Visual Studio. In order to figure out what the cryptic code 255 means, I ran this command at the command-line to see if there was additional output. I got:

"C:\Program was unexpected at this time.

It then printed my path and I noticed there were some entries with quotes. I removed the quotes in the path and tried again, and it worked. So the problem is that quotes cannot appear in your path to run the command as it is entered. I originally entered these in to appease Cygwin.