Do not use CS (cable select). It is error-prone on most systems. Jumper the drive at the end of the cable to master and the other to slave, if possible. The other way round should work, but BenQ recommends to do it this way and I think (hope) they know what they tell us.
And dont forget to set both drives on that ide port to "AUTO" or so in the PC BIOS for the first tests...
Maybe the CS setting also made the flash procedure fail ... in this case, look at
and their DOS flasher / winflasher to revive the drive.
CS is evil !
ANOTHER THING: Make sure the HDD on the IDE bus is NOT jumpered to master or CS - best config is one drive (end of cable) as master and the other one (in middle of cable) as slave. Normally, other configs may work but errors may be hard to find.
If possible, be sure to use a good 80pin cable. I have two writer on a 40pin std ide cable because the 80pin I had was a little bit too short, but I will change this ASAP.