Quicktime not compatible

Hello,

I was watching a series of mp4's from my thumb drive just fine and I went onto the next file on the same thumb drive it will not play. I'm getting an error pop up either the file is damaged or not compatible with Quicktime. As I go back to my previously played files on the thumb drive I'm getting the same message now. I've removed the thumb drive, tried again and it's still not working. I've done nothing different, no updates. Currently on Quicktime Version 10.4 and OSX 10.10.4. Everything seems pretty straight forward but I must be missing something?? Any ideas?