Thanks very much for all the tips - I went back to basics and started with a 'hello world' script which worked - then executed it via an html page.
In looking at the previous log files, they didn't show up any POST requests being sent. I re-uploaded the files using my own FTP (rather than the on-site uploader) and believe this may have done the trick. Although the 'uploader' assured me it had uploaded the scripts in binary - I'm not convinced. Anyway I now seem to have the scripts functioning - not necessarily correctly but functioning all the same!
Thanks very much for your help!