no reason - mp3s all good - tried readding. Only 10 out of 200…makes no sense.
So all the MP3s are in exactly the same location that they were in when you added them to the database, and you didn’t rename them?
Yep…makes no rational sense…can play them in winamp ok. Same format as the others. Deleting and reloading doesn’t help - still red.
The only reason why files show red is that the database can’t find them - meaning that they are either not in the original location any more, or they’ve been renamed.
Are you 100% certain that you didn’t move the files from one place to another after you added them to Engine Prime, and that you did not rename them after you added them to Engine Prime?
If he’s dragging and dropping them again to the crate then how the location can move?
Where did he say he was dragging and dropping them?
There must be some reason why they’re red. Something he hasn’t mentioned.
HERE ^
Delete from collection, reload again to collection - this is done by drag and drop.
Not necessarily. 
Are there any unusual letters? France letter for example? I had the same problem and renaming the file with “normal” letters helped.