I had originally bought a 740i, lightscribe didn't want to work at all. I have tried disabling autorun through the registry and the group policy editor, doing the registry dword fix/editing that was posted on here, nothing worked. took it back in, found an 840b for 10 bucks cheaper. decided to give it a shot. same problems. went through same fixes, same exact symptoms, etc.
In a last ditch effort i decided to try and swap the channels the drive was on; i had originally set it as a master on the primary eide channel (all my hard drives are sata). I switch it to the second channel, get into windows, try nero, it tells me there's no printer installed when trying to print the lightscribe label. I figured that was odd since it never said that before, just said the disc wasn't lightscribe or that it couldn't find it. I tried surething cd labeler, and low and behold, the thing is burning it's first cd-r lightscribe label.
I haven't swapped back to the 740i to check if this works for it too, but i'm fairly sure that by it being an LG drive also (just slightly different model number) it would have the same quirk. It makes no sense on why this drive would work any different on a separate channel, but it does.
Hope this helps others out there having these problems.