Sense Key Medium Error 0x73, 0x03

I have a 2011 Mac Pro 2.8 Quad core Intel Xeon with a dual optical drive. Running 10.6.8 Snow Leopard.

I have (2) LG Optical drives in there: DVDRAM GH24NSB0

I have had to replace this drives from time to time with new ones. I replaced both in May of this year. I was getting "Sense Key Medium Error 0x73, 0x03" messages when trying to burn discs with Toast titanium 10. Things were fine.

Then about a month ago, I was getting that error message with just the second drive. Went and replaced it. Still getting the error message. First drive still works fine.

I use Verbatim DVD-R discs only and always have.

I have tried burning at slower speeds. Still will not work.

The Buffer under run box is checked.

I don't know what else to do.

Suggestions?