Hi Yan,
Thanks for using our discussion forums. This sounds to me like MAX has been corrupted. I would suggest uninstalling MAX and the IMAQ driver and then installing IMAQ 3.0.1 from here:
http://digital.ni.com/softlib.nsf/954feaeea92d90918625674b00658b83/8e957f73e5b7c47086256f4d0058c162?OpenDocument
This should take care of the problem. However, if you still have any troubles, please let us know.
Regards
Dan Q
Applications Engineer
National Instruments