hello

after more than 1 hour of googling I coulnd figure out where the problem is
here are some detaills:

#dvd+rw-mediainfo /dev/hdc
INQUIRY: [SONY ][DVD+RW DW-P50A ][1.8e]
GET [CURRENT] CONFIGURATION:
Mounted Media: 10h, DVD-ROM
Current Write Speed: 1.0x1385=1385KB/s
Write Speed #0: 2.0x1385=2770KB/s
Speed Descriptor#0: 00/2298495 R@2.0x1385=2770KB/s W@1.0x1385=1385KB/s
Speed Descriptor#1: 00/2298495 R@1.0x1385=1385KB/s W@1.0x1385=1385KB/s
READ DVD STRUCTURE[#0h]:
Media Book Type: 25h, DVD-R book [revision 5]
Legacy lead-out at: 0*2KB=0
READ DISC INFORMATION:
Disc status: blank
Number of Sessions: 1
State of Last Session: empty
Number of Tracks: 1
READ TRACK INFORMATION[#1]:
Track State: blank
Track Start Address: 0*2KB
Next Writable Address: 0*2KB
Free Blocks: 2298496*2KB
Track Size: 2298496*2KB

#cdrecord -prcap dev=/dev/hdc
....
Device type : Removable CD-ROM
Version : 0
Response Format: 2
Capabilities :
Vendor_info : 'SONY '
Identifikation : 'DVD+RW DW-P50A '
Revision : '1.8e'
Device seems to be: Generic mmc2 DVD-ROM.
....

with growisofs I get
:-( /dev/cdrom: media is not recognized as recordable DVD: 10010

with cdrecord-prodvd:

Device type : Removable CD-ROM
Version : 0
Response Format: 2
Capabilities :
Vendor_info : 'SONY '
Identifikation : 'DVD+RW DW-P50A '
Revision : '1.8e'
Device seems to be: Generic mmc2 DVD-ROM.
./cdrecord-prodvd-2.01b31-i686-pc-linux-gnu: Sorry, no supported CD/DVD-Recorder found on this target.

anyone can tell me where the problem is?

I completely feel your pain. I had similar problems when I first purchased a LG GSA-4120b DVD burner. You might want to try different media; this does make a difference.

Also, only cdrecord-prodvd works for me; not dvdrecord or growisofs. This really irks me, because I generally want to avoid non-Free software. What are your cdrecord-prodvd command parameters?