Additional information:
My accesspoint has a single radio interface. It was configured WPA2-PSK Force CCMP (AES). I switched to a more compatible mode:
WPA/WPA2 PSK Mixed Mode, Auto Mode TKIP or CCMP (AES) Mode.

But this doesnt change anything.

Currently I am not able to use any wireless card. Not the internal one, nor the PCMCIA cards.
:(