I've had 1 7240 overheat and have issues, my other 2, a new 7240 and a 7260 have been fine so far, the 60 even burned 10 disks in a row at about the same conditions that cooked the first burner.
I still prefer them and got the other 2 when good sales were on as they are about the best quality fast burners around right now.
As far as your issue I have found some burners can only burn so slow and if you try to burn slower then it likes Nero will throw a error and trash the disk. I have ran into this more when trying to burn multiple disk at the same time using multiple burners, but think it applies to one at a time too.
I haven't tried any RW media yet with it so can't say if the issue I found applies to you but it is something to watch for with regular disks.
I'll have to try some soon and see what happens as I have some older4x verbatim DVD+RW disks that I think are 4x rated.
You might want to try the disks in another burner and box to make sure it's not the disks but any drive can go bad and they are supposed to have a 1 year warranty as far as I know though they weren't interested in helping me when mine got weird after about 5 month use, though they said I needed to take it up with the seller and new egg only offered a 30 day exchange on it.
Other users have had better luck though if you decide it needs to be replaced.