Ok, this is definately some kind of bug, I think the devs should have a look at this.
If this error occurs resetting Mediastore on the phone, replugging it and sync again solves the issue.
Stock Player and no Debug mode.

Ok I will write later if it did the job for me, thanks again for your help. But there seem to be a lot of issues with playlists, I read many threads with people having playlist problems. But not nearly enough to be a genereal issue, so I am asking myself what is going on here. I am pretty sure that ...

Did you ever test if resetting your mediastore data resolved your problems with the stock player sync.

Ok Kies is installed anyway. So I connect the phone in Debug mode and then sync normally with Monkey just as I did before, and use player pro for playing?
Any additional things to setup?
Sorry for dumb questions I just switched from Iphone to the galaxy and still have much to learn.

Ok thanks a lot I will give is a try. I found something about special drivers needed for the phone to be recognized in debug mode. Can't test right now, as I am not at home.
Where can I get them?

Are there any disadvantages of connecting the phone in usb mode?

Exact same issue here. Please help.
By the way absolutely perfect error description.