Your post was just found in another forum and moved here last night.
I suggest trying a different blank disc - do not use RW discs, especially one that has previously been erased as OneCare doesn't play well with them. Use the less expensive R type discs.
If you are still unable to proceed with backup, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator