Sony,
I would recommend making ssure you have the most up to date driver. Also, if you have installed any software or applications since you first were successfully using the USB to Serial adapter, try uninstalling that software. You can download the latest
USB to Serial Driver from our page (just scroll down to the bottom of that link).
If that doesn't work, I would suggest trying it on another computer to see if it causes the same problems. If other computers have the same problem it would probably be a problem with the adapter. If it works fine on other computers we'll know that it is an issue with the setup you have on the other computer and we'll need to look more into it.