Thanks a lot Dev.
In fact in the meantime I have solved the problem, I post here the process in case it can be useful for someone else.
Click on: Start >> Control panel >> Add remove programs >> NI software >> Change.
From the list select NIDAQmx. Click on "Repair" and insert the CD that comes with the DAQ board. When the repair process is finished, select Measurement and Acquisition explorer, click on "Repair" and do the same. Reboot the PC. Now it should work.
Bye and thanks again. these forums are great.