Hello and thanks for your reply.
I bought the uTrack24 two weeks ago, and immediately updated the firmware to version 3124.
As long as I don’t delete anything, the uTrack24 works fine!
(It might be that the operating system inside the uTrack24 expects a file on the USB drive that it ‘knew’ it was there, but is now gone after the deletion of the multitrack session(s). Just guessing….)