Hi Marco,
I also mailed, but maybe this is a better way so everybody can learn from my mistakes 
The firmware is the burner is 043, using nero 5.5.10.33 (bundled with your burner).
My standalone player is a Kiss DP-500 (http://www.divxspeler.nl/N_frame.html) a DVD player with DIVX decoder in it 
I tested a cd (datawrite) with the scandisk tool from nero and it failed also 
About the standalone player, I tested the successfull cd’s on my KISS player and on a Pioneer DVD player and they both didn’t accept them.
I live in Holland, please give me a name of a shop were I can order good dvd-r of dvd+r dvd’s 
Thnx in advance, below you will find the DVDInfoPro information from the current DVD’s I own.
Martijn
Verbatim:
Media Information
Region information N/A not a DVD-VIDEO
Media code/Manufacturer ID MCC 002
Format Capacity 4.38GB(4.70GB)
Free Blocks 405405696
Free Capacity 4.38GB(4.70GB)
Book Type DVD+R
Media Type DVD+R
Media Id Code Speed 4.0x 5540KBps
Available Write Descriptor CLV 4.0x 5540KBps
Available Write Descriptor CLV 2.0x 2770KBps
Available Write Descriptor CLV 1.0x 1385KBps
Data area starting sector 30000h
Data area end sector 23053Fh
Linear Density 0.267um/bit
Track Density 0.74um/track
Number of Layers 1
Datawrite:
Media Information
Disc Regions are 1,2,3,4,5,6,7,8
Media code/Manufacturer ID PRINCO
Format Type UDF 1.02
Volume Name PLOP
Application id
Implementation id AHEAD Nero
Recording Date/Time (mm/dd/yyyy) 11/ 9/2003 20:16:35
Format Capacity 4.09GB(4.39GB)
Book Type DVD-R
Media Type DVD-R
Media Id Code Speed 4.0x 5540KBps
Available Write Descriptor CLV 4.0x 5540KBps
Available Write Descriptor CLV 2.0x 2770KBps
Write Strategy Speed 4.0x 5540KBps
2x Speed OPC beta 09
2x Speed OPC power 13
2x Write Strategy field 1 11 87 78 80
2x Write Strategy field 2 88 80 00 00 00 00
4x Speed OPC beta 01
4x Speed OPC power 1B
4x Write Strategy field 1 0D 0F 0B 08
4x Write Strategy field 2 97 08 0F 0C
4x Write Strategy field 3 00 00 00 00
4x Speed OPC beta multi-pulse 00
4x Speed OPC power multi-pulse 00
4x Write Strategy field 4 00 00 00 00
4x Write Strategy field 5 00 00 00 00 00 00
4x Write Strategy field 6 00 00 00 00 00
Data area starting sector 30000h
Data area end sector 20BDCFh
Linear Density 0.267um/bit
Track Density 0.74um/track
Number of Layers 1
Princo:
Media Information
Region information N/A not a DVD-VIDEO
Media code/Manufacturer ID PRINCO
Format Capacity Not Formatted
Free Blocks 412352512
Free Capacity 4.38GB(4.71GB)
Book Type DVD-R
Media Type DVD-R
Media Id Code Speed 1.0x 1385KBps
Available Write Descriptor CLV 1.0x 1385KBps
Write Strategy Speed 1.0x 1385KBps
Data area starting sector 30000h
Linear Density 0.267um/bit
Track Density 0.74um/track
Number of Layers 1