Okay... for those that were interested, have sorted this at last.

It would appear it was a problem of my own making... (awaiting the collective groan) basically the *server* I have Sharepoint installed on has 2 drives available, C with 6Gb and E with 36GB. In my wisdom I had decided to try to use E:\inetpub\wwwroot as the 'home directory' for the Default Web Site by changing it in the properties of IIS. Almost as a last resort I changed this back to C: and after a reboot of the server things started working.

As an extra point, my journey through trying to resolve this has revealed an interesting tip. For those that are trying to glean the public key token for your dll using the "sn" utility. Don't use -t as it states in much of the documentation as this gives the wrong token, use -T.

Thanks to those that took time to reply to my original cry for help.