As BrowserUK said, 9984 is not a standard Windows error code, but you don't say anything about the program you are running, or where you get the return code from, perl, open, system, or $?. Did you shift the return code right by 8 bits? 9984 >> 8 gives 34, which is ERROR_WRONG_DISK. Don't trust that too far, the application can return any old number that takes its fancy, it does not have to use "standard" Windows error codes.