Make sure that the baud rate settings in the TS-590SG for each of your connections are the same in the rig and the software. The defaults are set at 9600bps, 1 stop bit for the COM port, and 115200 and 1 stop bit for the USB port. These are adjusted via menu item 67 and 68 in the TS-590SG, however it is easier to simply set the matching values in MLDX. If you change anything in the rig, you need to turn it off and then back on for the changes to take effect. Also, make sure you're using the right kind of cable (if you have one) between the TrippLite and the COM port on the back of the rig. The connection requires a straight-through cable, not a null-modem (crossover) cable. I presume that if you were to try and connect MLDX through the USB port, it works just fine? If so, perhaps you should connect your other software through the COM port. Remember, only one piece of software can access the port at a time, so MLDX and your other software will need to use separate ports on the 590SG, so double-check that you haven't inadvertently assigned the same port to both software packages. I found the connection for the 590SG to my Mac to be very straight forward, not that this helps you much. Any problems are usually caused by something small but important: baud rate and the selecting the wrong port are probably the most common.