Do you have to use Toast? It could just be having a software hiccup, try using the Finder's burning feature or Disk Utility. For shits and giggles, try repairing permissions. After that I'd probably try either another OS X install(on another hard drive/partition) to see if OS X itself on the boot drive is screwed.

After that I would look into replacing the drive. If I'm wrong, someone else correct me.