That may be due to a problem with the windows driver. Try reinstalling it or seeing if there is a later version available. What is being shown in MAX and windows device manager? Is it a com port? Can you communicate to it in MAX or with another terminal emulation program (hyperterminal, putty, etc.)?
Are you able to make a screenshot of the VI? I always get an error message by VISA READ.
Thank you for your reply.