DVD-R Burn Failed (medium write error)

Anybody let me know what I'm doing wrong?

Exported 30 minute video out of iMovie in iTunes

Appears under Home Movies

Create New Playlist

Add Movie to Playlist

Burn Playlist to Disc

Disc Burner: OPTIARC DVD RW AD-5690H

Preferred Speed: Tried Maximum, 16x, 12x, 8x & 1x

Disc Format: Data CD or DVD, right?

Burn

insert SONY DVD-R 4.7GB 1x-16x

"You inserted a blank DVD. Are sure you wish to create a data DVD?"

Burning Disc...initializing

Writing "movie" (for several minutes)

Burning Disc... finishing

Disc gets ejected along with the medium write error shown above.

Any HELP appreciated...

Thanks!