I was running the program under a limited user account on XP and the program was set to save the listings file to the root of c:\ drive. Changing the program to save to 'My Documents' didn't produce any error and the xml file was saved normally.
Thanks for replies, I have full admin rights but changed XML file write location to My Documents, it worked straight off. Put the location back to where it was originally in the XMLTV prog dir.. worked again. Something corrupted I s'pose. All ok again cheers fellas.