Ok, thanks. I finally solved this problem by just testing.
But other problem occurs still (and that was one reason for not getting stuff to work):
If I run my vee program, all is ok (devices are opened, and I can read and set values), and call to closeunit() gives return value of 1 (so unit is closed), and leds on units turns off. But if I after that start again that vee, nothing happens (vee freezes), only thing that helps is to remove and plug back units to usb port. After that one time works again, and after that problem occurs again ...
Any ideas ?