The only other thing it could be is a handshaking signal problem (RTS, CTS, CSR, DTR, CD). All of these lines should be high. You need a breakout box to see this. A breakout box is a device that plugs inline to the serial cable and displays the condition of the lines with LEDs. If you are going to work with serial ports, get one. They don't cost much at all. Available from Radio Shack and most electronic stores (CompUSA, etc). I can't see anything else that would prevent the data transfer. Make sure you have the com ports configured correctly and enabled in the BIOS. Check that the VISA names are correct. The code looks right. Maybe try to enable the termination character. Also try concatenating a new line constant to the end of the write string. This might be the answer.
