You are absolutely right.
I tried to format the stick with ExFat, hoping the files won't get splitted after 4 GB.
So this is the reason for this error message, then.
Thank you!
By the way: I am right now just testing the box from a collegue and I only want to buy it, when it's possible to record properly.
Do you think, this will be possible any time soon?
Like: Entering a time and a channel and letting the box record a few hours on this channel etc?