2012 Head Unit not playing certain mp3's from USB drive....??

I have a number of mp3's on a USB drive and the head unit won't play certain ones. I've searched to no avail. I'm not the sharpest tack in the box when it comes to these matters. The mp3's in question do play on my pc. What am I missing?

2012 stock head unit....

 

Check to see if you have any capital letters in any part of the file name or extension.
Also for some reason files can get corrupted. Try downloading the same songs again...

 

I have to check more but could it be that those files that don't play on the HU have an issue with permission or they're blocked? Being that those files in question do play on my pc, I'm thinking they aren't corrupt (but I could be wrong).....