Just found a new firmware (version a110) for GSA-4120B on the net. Check it out :)

The new firmware claims to fix compatibility problems with Lite-On DVD-ROMs.

check this thread for more info: http://forum.rpc1.org/viewtopic.php?t=29393&sid=338c3237008309a9458192abf9d8bb76

Grab the firmware from:

http://www2.melcoinc.co.jp/pub/hd/dvsmd5812fb_fwa110.exe

And as always, if it's not broken, DON'T FIX IT !