Control HP Pro Curve 4000 M per Serial Port

[schwerdy]

Hi all,

I want to control a HP Pro Curve 4000M with the Serial Port on a Linux
machine. The first time i did it with "$ screen /dev/ttyS0" - it
worked perfekt, but after finishing my session, I had to kill the
screen process manually. From this moment, controlling was impossible.
After typing "screen /dev/ttyS0" the cursor jumps to the top-left and
nothing else happens...

I supposed there could be an old lockfile, but /var/lock is empty.
Does anybody know what's going wrong?

Thanks in advance,
Schwerdy