DVD_burning Error_Illigal Request

[laurita]

Hi, I'm trying to burn a data-DVD, for my backup's.
I've done this many times before with no errors!
Application = Titanium Toast 6
But yesterday I got:
Sense Key = ILLIGAL REQUEST
Sense Code = 0x21, 0x02
BUFFER UNDERRUN

I tried it many times but everytime it stops burning after 5 min. and gives me this message.
I have a dual 1.8 G5, Mac OS X 10.3.5, 1.5 GB DDR SDRAM
The DVD recorder Pioneer DVD-RW DVR-106D
Does anyone know how to fix this?
Thanx!