I don't think this error would be produced by a bad connection (that would more likely give a timeout when the read command didn't get back what it expected). Are you sure that no other software is trying to access the same serial port at the same time? If you've been using Hyperterminal or anything else to test communication, you need to close it before communicating in LabVIEW. Also, are you absolutely sure you're using the right VISA resource name for the port you want?
