Thanks for your reply!
I'm attaching to this post two text files with excerpts taken from the Output Window and Script Editor, so that you can check the error messages.

Could you please also indicate where I can get more infos on this Slim scripting you mentioned, or about that box in the shader window? Anyway, I will give it a look as soon as I can put my hands on Maya this evening...

For the moment thanks a lot for your time. It's really appreciated.

Cheers,
Mark