Now, still not got to the bottom of why XML ain't working on our live server:
However, in parallel to this (since it is working on our development server) I'm having some encoding issues. I've found this resource (which looks great):
The problem I have is that I'm outputting this XML in to web page using ASP, but the ASP is automatically altering the encoding from ISO 8859-1 to UTF-16. It seems that's the standard, fine, but my XHTML is in ISO 8859-1 and it's screwing up the source and page display by spacing out the code generated by the XSL, adding a new XML declaration (which I guess will kill the validation) and causing IE to display the BOM (Byte Order Mark).
There's an "Objects/Interfaces encoding" section at the bottom of the page I've found (see above)... I'm using method 5. But I don't want it to be converted into UTF-16 encoding and I don't want the extra XML declaration to appear in the output. One more thing. We're not hosting this site, so we're unlikely to be able to do anything that involves needing read/write permissions to a directory very easily. Any ideas?