Thanks Ralph!

The problem was in the cable. After connecting the 7. and 8. pins with a small jumper on the serial end, all freezings disappeared Since I am not a hardware expert, it really was scary to make a step like that, but it works! And now I remember, that my cable is not a Korg product, because as far as I remember I bought it from Roland, so you might be wrong when you think that Korg does not do it's best -though it took them quite a long time to make this driver anyway.
Otherwise I am looking for someone using NS5R to share infos on the unit. I am eager to know, how people use RPN/NRPN messages, and I would be happy to share everything I've learnt on this instrument. Or can anybody tell me where I can find such forums?

Thanks:
redeye22