Thumb drive problem

I have thumb drive which when I copy MP4 clips to it, renders the files un-readable. I have tried repairing with disk utility but doesn't seem to work. Any ideas?

Using an IMac by the way

How large (what file size) are these files? Are you able to successfully copy other types of files to the drive and have them open properly? I assume the files will copy/play properly if they are copied somewhere else (such as the hard drive)?

File sizes are 200-600mb, and yes other file types copy and open properly. The MP4 files in question are being copied from the hard drive to the usb thumb drive. The files play fine from the hard drive...it is when they are copied to the thumb drive where the problem occurs.

Do the files have the proper 3-letter extension? If not, the system could be confused as to what kind of file they actually are, and refuse to open them properly.

Yes they do have the .mp4 extension. I'm thinking of reformatting the thumb drive and starting fresh, or maybe a new one altogether.

Just a thought had a similar problem with FAT 16 once if its FAT 32 it should read and write on anything.

Thes flash drives are like the memory cards in cameras. It is usually recommended that one completely reformat the card after every complete download of pictures into a computer, or every month or so if you can.

Flash drives are the same. The memory in the chips is volatile and needs to be cleared out to start again fresh every once in a while.

If you eat the same bread out of a plastic bag and keep putting new bread in without eating all the old bread, it will get stale and eventually moldy. You clearly have some moldy data in that drive.