That's a timeout error. Either the instrument sent nothing or you specified on your VISA read too many bytes to read and the intrument didn't send that many. If you're not seeing any characters returned, verify that you're sending the correct command and that it is properly terminated. Most serial instruments require that you terminate each command with something like a carriage return or line feed. If you're receiving soomething, instead of using a fixed byte count for the VISA Read, first use VISA Bytes at Serial Port and wire the output of that to the VISA Read function.
