It's been many, many years since I've had to actively support windows, but from what I remember, the two different Window codebases (the NT derivitives, vs. those that derived from DOS) used different calls to get to a shell. One of them used cmd while the other used command. (I have no idea what the file extensions were ... they might've been exe, com, or any of the other executable extensions in windows ... I also can't remember which was which)

So, when one doesn't work -- try the other one. (if you had mentioned what version of Windows you were using, someone might be able to elliminate this as having been the problem).