Lite On LTR40125S

I have a Lite On LTR40125S which is 48X/40X/12X. I purchased some
Memorex High speed CD-RW disks with recording speeds up to 12X. I am
using Nero 5 as that is what came with the burner.

I am able to erase these disks, but after what appears to have been a
successful; write, it throws the Lite On LTR40125S into a locked up
mode which I cannot do anything in windows until I remove the disk.

I have the latest firmware as I checked and even though the file was
supposed to be newer, it was the same size and date of an older
firmware I installed.

Did I buy the wrong disks for this burner? Any other suggestions
appreciated.

Thanks