hi marc thanks for the help.
i think the akai mpk49 is sending some midi controls on its own to cubase 5.
It sends panorama and volume ctrls to the active track.
i tried to unplug the mpk49 and the transmission stops.
the problem is that the keyboard seems to work perfectly with reason and also with cubase 5 if the virus ti snow is disconnected...
I also tried different connections:
VIRUS TI -> PC usb1 mpk49 -> PC usb2
VIRUS TI -> PC usb1 mpk49 -> VIRUS TI midi IN
VIRUS TI -> PC usb1 mpk49 -> PC usb1 and -> VIRUS TI MIDI IN
but the problem remains..