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There are several methods I've used to 'reset' my Pioneer so it will burn again.
1. Try different brands of media. 'Slower' media seems to work best for some reason, 8X max. I've had some success with 16X, but the burner can only burn at 4X speed.
2. Try a dvd-rw disc. The media must be either 1X or 2X. Discs marked 4X will not work.
3. Try a hard reset (unplug, wait a couple minutes, plug back in)
How many discs have you burned (approximately)?
What's the internal temp?
Do you burn a bunch of discs all at once? If you do this, you might be overheating the unit. Give it a rest between burn sessions.
Hope that helps,
1+ Pioneer DVR-810H-S
1+ Pioneer DVR-57H
1+ Toshiba RS-TX20
1+ Humax DRT400
1 Humax DRT800
Most with Lifetime and upgraded drives
All Series 2s with Linksys USB200M