I had the exact same problem. My QPS Firewire 8x4x32 CD-RW drive worked fine under the OEM version of Toast 4.0.1 that came with the drive, but when I bought the Deluxe 4.1.2 version, the drive was no longer recognized by Toast.
Turns out there is an extension conflict between Toast's drivers and the Que! Fire extension. I disabled the Que! Fire extension and everything now works fine.
Hope this helps in your situation.