Prohosting works fine for me...I haven't tried Netfirms so I can't verify for that, but prohosting was pretty easy for me to run my scripts on.
What FTP client are you using to CHMOD the files?
This might seem like a very silly question, but on Prohosting, did you CHMOD all the files to 755? Because regardless of what the directions for the script say, you have to change them all to 755 on prohosting.
Hope I helped and that I'm not just talking rubbish as usual