I just noticed when you first wrote out the path you wrote c:/windows/startup.
the slashes go the other way in windows c:\windows\startup...
Unless you are using the code I posted for you, post the actual code you are using...
I'm not sure what you mean by restrictions? are you on a school network or something?
Check to make sure the actual path exists at the command line just write
if exist c:\windows\startup echo yes