i have had this problem with USB > serial converters before, and 99% of the time it can be fixed by changing which com port the device is assigned to from device manager (change it to com1 or com2) some programs have issues talking to com8 etc, that they are normally assigned to.
From the device manager window, double click on the USB serial port. click the port settings tab and click advanced. select com port 1 or 2 (it will tell you if they are in use) click ok twice and you should be good to go.