First, make double sure that you have the 166S and not the 165H or 163 or 163D. I assume you do, but it never hurts to double check. Also, you didn't specifically mention it, but make sure your drive is on the motherboard's IDE bus and not an add-on PCI IDE controller. Some PCI IDE controllers don't work properly with optical drives.
If you are running nForce IDE drivers, that could be the source of the problem as well. Switching to the generic MS drivers often helps for problems like this.
If you have been happy with the nForce drivers, you haven't had any other odd problems with your optical drives, and you really don't want to change them, then I would try flashing the drive from DOS. You can get the binary from digi's page, along with Mtkflash and a DOS boot disc maker:
Follow the "The LiteOn/JLMS DVD's pages" and "Binary firmware, Mtkflash, Dos floppy" links to get to the page which has a bunch of different binaries and the other utilities you will need.
Download the DOS boot disc maker and make a boot floppy if you don't have one. Then load Mtkflash and the binary to the floppy. Next, read the instructions for how to use Mtkflash by following the "How to use MtkFlash" link near the top of the binaries page. In particular, make note of the position of your drive on the IDE chain so you know which number to supply to the Mtkflash commmand line.
Then reboot to the floppy and run mtkflash. That should do the trick.
Isn't digi's site a great resource?