Disk Utility Burn button is grayed out

I was happily burning some DVDs, and the 7th one, the burn icon was grayed out. I deleted the preference files, restarted the computer, tried to burn using different disk images under different users, and still, it is grayed out and won't let me burn anything at all.

Any suggestions?! I'm supposed to be leaving my house in 10 minutes with four more DVDs!