Can't burn DVD's but able to burn CD's

[cabbage]

I have this strange issue the last couple weeks. I have a PowerMac G5 with a built-in Sony DVD burner. I also have a 12" PowerBook and a Lite-On DVD Burner that I've put in a firewire enclosure. Both of these DVD burners have been running fine for over a year. Now all of a sudden I'm not able to burn DVD's on either unit. I'm using the same Verbatim and Sony 1x-16x DVD-R that I've been using and burning with th elast several months.

With Toast 7.1 when I start burning the writing lead-in text is displayed for a second and then it goes straight to writing lead-out. A popup say the disc failed with error -50.

In DVD Studio Pro burns fail also. I've tried the Lite-On burner on the PowerMac G5 and that fails. Both strangley can still burn CD's without any problems.

This is really weird. Anyone have any ideas on what I can try next?