I stumble upon a "workaround" almost immediately after posting this! ) only downside is that seeking isn't supported, but I can live with that until a better answer can be found!
Simply renaming the .mp4 files to seems to "fix" the problem of not being able to play the files.
Most CD's don't come with track and artist information included, so this information is downloaded from a central database.
Anyway i recently got myself a new 8GB SDHC card to replace my dead 4GB SD card to use in my Dopod D810.
After using it for a bunch of MP3s, it became obvious very quickly that i needed to cleanup my music collection and update the meta data so they would be sorted correctly in the mobile media player.
To my surprise though, the changes are not automatically applied to the files on disk, leaving the WMP database of information out of sync with the underlying files. although personally i think the small delay required to update ~10 files would hardly be noticed amongst the above process.
Anyway, you apply the changes to the underlying files using the Library - Apply Media Information Changes option.
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