I just encountered the same problem with RC1... Sure hope the problem goes
away with the full version I get tomorrow. But searching the net I found this
work-round:

Hey Everyone,

If you set your system clock to before October 31st 2006, you will be able
to burn:

1. Right-Click the clock on the taks bar

2. Select Adjust Date/Time

3. Press the Change Date-Time button

4. Pick a date before October 31st 2006

If this doesn't work, then it is caused by some other computer problem.
Check your decoder and DVD burner.

Posting it here just n case it hasnt gone away in the RTM!