@MATT1971 > Firstly, I just want to double check even though you said the other USB devices works; but are you sure it is only the USB device that is crashing Rekordbox, and not another reason?
If so, it is most likely a file was corrupted on the drive. Some possible solutions I can think of are, open the USB device on your computer without Rekordbox, and try to scan through your tracks on the drive using an app such as MP3 Scan+Repair for Mac, or something similar for Windows. This can detect if a single file may be corrupt and is causing the fault.
If you find any corrupt files, you should remove them from the drive, then try to open Rekordbox again. If you're able to get it working, you can then re-add the track/tracks back to the drive. If Rekordbox crashes again, it might be necessary to continue scanning the tracks.
It may also be something embedded within a file, such as the artwork, but if Rekordbox keeps crashing, you may only be able to access the file through another application such as iTunes, where you can replace or remove the artwork on files. This is hard to determine though and is a lot of work to do for every track.
If you would like to bypass all of that and save time, the best thing to do might be to re-format the drive entirely, and re-export your playlist or library from Rekordbox to the drive.