Burn Underrun error from iTunes



I am having a lot of trouble with the error message “The device drained its buffer without burn underrun protection” when trying to burn CDs from iTunes 4.6. My iBook has OSX 10.3.4 installed. The burn fails and the cryptic message pops up every time. The machine has 640 megs of memory, and the 40 gig hard drive is only one third full. I think this may be a system problem, beacuse I am unable to burn CDs from the finder, or from any app for that matter.
The problem started when my son dropped a sock (!) and it fell on the screen of the iBook when it was burning a CD. The burn failed and ever since then I have had trouble burning. All the usual recommendations don’t help: burning at a slow speed, using different media, logging out and burning with a different user account. I wonder if it is possible to re-install the firmware for the CDR drive? The drive is a SONY CD-RW CRX821E. Thanks for any help!