Exactly what mufasa said.
you can test this by moving the engine folder off of your drive and then connect to the players or engine software. If you don’t get the error you know something in your engine library folder is corrupt.
Now if you move forward without the engine folder you will loose all your hot cues and loops and crates/playlists etc.
I recommend making weekly copies of the engine library folder and keeping them in a folder somewhere on your computer. I usually make a copy every time I edit tracks or after saving hot cues while playing on the players.
I name them with the date. for example
Denon Backup Folder and inside that folder are other folders with dates that I backed up.
1/26 Backup , 1/29 Backup , 2/2 Backup etc
The reason I keep multiple folders with multiple backups is because if you just keep one backup and have a corrupt hip hop song but have only been playing house songs you might not know it.
In that case you would restore the engine folder that has a corruption on it.
This is really covering everything but multiple copies means you can keep replacing the engine folder with different backups moving back in time until the problem resolves and only LOOSE the minimum amount of settings/hot cues etc.
hope this makes sense I will be doing a tutorial on this as I found out the hard way of not doing it like this as I feel you might have the same thing going on.