The situation atm. is as following :
updated firmware on pixhawk v2 with newest stable ardusub and it wont connect. If i update with any of the other firmware for rover, plane etc. it works with no prob and i can start the calibration.
after the above steps i tried uninstalling gqc and formatted, fat32, the 8gb sdcard in the pixhawk and repeated the above but with the same result - no connection with the pixhawk. the main led doesnt blink at all with ardusub but behaves normal, blue constant, with the other firmware available.
read another thread with a person with same symptons but that thread died out before any real conclusion, hope you guys can help. thx in advance.