I have quite a few USB cables just laying around here doing nothing so it was an easy swap for me.
When I started out yesterday, I just grabbed a random USB cable with the correct ends to fit a TIU for updating, so it's status was unknown.
I also reread the thread and see you have a USB to Serial cable, mine is just a straight USB connection to a Rev L TIU. I suppose the Serial to USB cables can go bad as well?
What's odd about yours is that it just worked last week with your TIU and doesn't work this week? That kind of makes me wonder if the cable is really the problem? Did you try another USB port on your PC and tell the Loader to Search for the TIU? If not I would try that first, before buying another cable.
Hopefully you'll get lucky like I did. Sure hope you don't have a hardware problem that requires your TIU to be sent out somewhere for repair.