Asset files were added to X3 for Gobbler integration. Platinum lacks Gobbler integration at the moment but still appears to have hooks in the program for the feature. I don't use Gobble and have "Save Asset Manifests with Projects" disabled in Preferences > File > Advanced. Enabling the feature in Platinum creates the files.

 
Ah, I see.
 
How do you know all this stuff

It is a curse

 
Just to add, Steve you're a genius
 
I just disabled "Save Asset Manifests with Projects" in X3, opened the 'offending' template and resaved it. I copied it across to the Platinum Templates folder and it now opens perfectly.

I am having a problem with missing audio files also. When I search no files found and when I skip I may get one or two tracks.What is the best way I can find and restore tracks?