Assuming that no one has fooled with your gear since the last time you used it, try the following:
1) Unplug the USB-to-Serial adapter, both from the USB port and its power supply.
2) Shut the computer down. Not restart, you want to do a cold reset-everything-in-the-box, which means shutting the computer down.
3) Now restart the computer.
4) Plug in the USB adapter's power supply.
5) Now plug the USB device into the computer. If you're running XP, you should get a "ding-dong" sound as the operating system recognizes the device.
6) See if CodeWarrior recognizes the port now.
I use XP and it seems after some length of time it randomly tosses it cookies on handling USB devices. There's no warning, the interface just stops working. My apologies if you've already tried this incantation.
---Tom