Problem with BenQ DW1620

I got a BenQ bulk drive DW1620 (G9Z7 firmware) a few month ago. I have no problem burning CD/VCD/DVD using Nero 6.6.x.x the lastest one. Recently right after I finished burning a DVD image, there’s problem everytime I try to burn a VCD. The problem is weird too. Usually the lowest speed for me is 12x, then all the sudden I notice the lowest speed now is 8x. Didn’t pay much attention to it, I select 12x. After the CD is complete, Nero will pop up a menu saying the burning process is 100% complete. After I click OK, then Next to go to the next menu, Nero will ask you if you want to save the progress, I select NO. Usually the drive will eject your completed CD, in my case the drive didn’t and Nero menu become all white and not responding. I can’t do anything but to reboot, and it take like 5 minutes for windows to respond. I check the CD afterward, it’s fine. Next I try to burn it at 8x, samething happened. When I backup my data to CD and DVD, I have no problem at all. Does anyone know what really happen? Does it have to do with the DVD image I burned is a region 3 disc?