"Formatted" is the key word here. CD and DVD blanks should not be formatted as this would only be valid for packet writing software such as InCD or DirectCD that come with Nero and Roxio, respectively. If you have either of these installed or a similar product that format blank CD/DVD media and allows you to write to them as if they are floppy or hard disks, you need to remove that application.
OneCare can write to RW media, but usually not erased/reused discs. You are better off using the much cheaper write-once media both for cost and for reliability.
-steve