I have the same issue. Originally my 1633S drive was running with the CS0C firmware version. I upgraded the firmware to the last release avaialble and then, the drive was not able to read any CD-RW media, only few CD-Media and the DVD media is working normally. I changed back to the original version provided by the "codeguys" unsuccessfully. Then I tried to use all the version provided by the codeguys and now the drive still with the same issue.
I don't know what to do....
If somebody can provide a workaround on this, please let me know.
BTW, can somebody tell me the the best drive I can use replacing this drive (I mean the drive with less problems than the Liteon drives)?