Nice idea....however that has not fixed the issue. I even tried moving the movie folder to a non-mapped network drive.
What I did notice was that Thumbgen can parse the TGMD data correctly (i.e. the NFO file contained within). The main difference between the XML file and the NFO version is the presence of some XML Schema statements at the start of the NFO i.e.
<movie xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" ThumbGen="1">
This is NOT present in the XML file saved to disk and used by WDTV for the Moviesheet. If I manually insert the above statement in the XML file (and the corresponding </movie>), then the error in the log file is cleared.
Unfortunately, Thumbgen still will not display the contents of the XML (i.e. Info Source : My own movie info (from .nfo file)) and of course when I then generate an updated Movie sheet and metadata, the file reverts to the version without the Schema instance statement.
I guess I'm just going to have to put up with this...ho hum.