This is a dvd-burner contained in my Sony VAIO notebook PCG-GRV616S.
At first everything went right. Then I started to install several burning sw to try. Now I can burn only dvd-rw. No more dvd-r burning with any sw!
These same dvd-r were burned previously without problems.
A message appears after a few seconds.
This is a error log generated by Nero 6 (hope it's not too long) making a backup of a dvd:

Windows XP 5.1
IA32
WinAspi: File 'Wnaspi32.dll': Ver=2.0.1.59, size=160016 bytes, created 05/03/2003 23.49.54
ahead WinASPI: File 'C:\Programs\Ahead\nero\Wnaspi32.dll': Ver=2.0.1.59, size=160016 bytes, created 17/06/2003 15.25.04
Nero version: 6.0.0.9 (Nero Express)
Recorder: <SONY DVD RW DW-U50A> Version: 1.5a - HA 1 TA 0 - 6.0.0.9
Adapter driver: <atapi> HA 1
Drive buffer : 8192kB
Bus Type : default (0) -> ATAPI, detected: ATAPI
CD-ROM: <SONY DVD RW DW-U50A >Version: 1.5a - HA 1 TA 0 - 6.0.0.9
Adapter driver: <atapi> HA 1

=== Scsi-Device-Map ===
DiskPeripheral : HITACHI_DK23EA-60 atapi Port 0 ID 0 DMA: On
CdRomPeripheral : SONY DVD RW DW-U50A atapi Port 1 ID 0 DMA: On
=======================

AutoRun : 1
Excluded drive IDs:
CmdQueuing : 1
CmdNotification: 2
WriteBufferSize: 74448896 (0) Byte
ShowDrvBufStat : 0
EraseSpeed : 0
BUFE : 0
Physical memory : 510MB (523244kB)
Free physical memory: 212MB (217940kB)
Memory in use : 58 %
Uncached PFiles: 0x0
Use Static Write Speed Table: 0
Use Inquiry : 1
Global Bus Type: default (0)
Check supported media : Disabled (0)

3.8.2003
UDF/ISO compilation
22.45.10 #1 Phase 112 File dlgbrnst.cpp, Line 1843
DVD-Video files reallocation started

22.45.10 #2 Phase 114 File dlgbrnst.cpp, Line 1843
DVD-Video files reallocation completed (no file modified)

22.45.10 #3 Text 0 File Isodoc.cpp, Line 5748
Iso document burn settings
------------------------------------------
Determine maximum speed : FALSE
Simulate : FALSE
Write : TRUE
Finalize CD : TRUE
Multisession : FALSE
Burning mode : DAO
Mode : 1
ISO Level : 1 (Max. of 11 = 8 + 3 char)
Character set : ISO 9660
Joliet : TRUE
Allow pathdepth more than 8 directories : FALSE
Allow more than 255 characters in path : FALSE
Write ISO9660 ;1 file extensions : TRUE

22.45.10 #4 Phase 111 File dlgbrnst.cpp, Line 1843
DVD-Video files sorted

22.45.10 #5 Text 0 File Reader.cpp, Line 118
Reader running

22.45.10 #6 Text 0 File Writer.cpp, Line 127
Writer SONY DVD RW DW-U50A running

22.45.10 #7 ISO9660GEN -11 File geniso.cpp, Line 3854
First writeable address = 0 (0x00000000)

22.45.10 #8 ISO9660GEN -11 File geniso.cpp, Line 3854
First writeable address = 0 (0x00000000)

22.45.10 #9 Text 0 File Burncd.cpp, Line 3173
Turn on Disc-at-once, using DVD media

22.45.11 #10 Text 0 File DlgWaitCD.cpp, Line 228
Last possible write address on media: 2298495 (510:46.45)
Last address to be written: 2269871 (504:24.71)

22.45.11 #11 Text 0 File DlgWaitCD.cpp, Line 233
Write in overburning mode: FALSE

22.45.11 #12 Text 0 File DlgWaitCD.cpp, Line 1722
Recorder: SONY DVD RW DW-U50A, Media type: DVD-R
Disc Manufacturer: MAMEG0 - 2
Disc Application Code: 64, Disc Physical Code: 193

22.45.11 #13 Text 0 File ThreadedTransferInterface.cpp, Line 768
Setup items (after recorder preparation)
0: TRM_DATA_MODE1 (CTransferItem)
2 indices, index0 (150) not provided
original disc pos #0 + 2269872 (2269872) = #2269872/504:24.72
relocatable, disc pos for caching/writing not required/required, no patch infos
-> TRM_DATA_MODE1, 2048, config 0, wanted index0 0 blocks, length 2269872 blocks [SONY DVD RW DW-U50A ]
--------------------------------------------------------------

22.45.11 #14 Text 0 File ThreadedTransferInterface.cpp, Line 937
Prepare recorder [SONY DVD RW DW-U50A ] for write in CUE-sheet-DAO
DAO infos:
==========
MCN: ""
TOCType: 0x00; Session Closed, disc fixated
Tracks 1 to 1:
1: TRM_DATA_MODE1, 2048/0x00, FilePos 0 307200 4649005056, ISRC ""
DAO layout:
===========
__Start_|____Track_|_Idx_|_RecDep_|_CtrlAdr_
-150 | lead-in | 0 | 0x00 | 0x41
-150 | 1 | 0 | 0x00 | 0x41
0 | 1 | 1 | 0x00 | 0x41
2269872 | lead-out | 1 | 0x00 | 0x41

22.45.11 #15 Phase 24 File dlgbrnst.cpp, Line 1843
Caching of files started

22.45.11 #16 Phase 25 File dlgbrnst.cpp, Line 1843
Caching of files completed

22.45.11 #17 Phase 36 File dlgbrnst.cpp, Line 1843
Burn process started at 1x (1.380 KB/s)

22.45.11 #18 Text 0 File ThreadedTransferInterface.cpp, Line 2130
Verifying disc position of item 0 (relocatable, disc pos, no patch infos, orig at #0): write at #0

22.45.11 #19 Text 0 File dlgbrnst.cpp, Line 1703
Set remaining time: 56:02,643 (3362643ms) -> OK

22.45.11 #20 Text 0 File DVDR.cpp, Line 1485
Recording mode: Sequential Recording Mode

22.45.11 #21 Text 0 File Mmc.cpp, Line 18724
Set BUFE: Power-Burn -> ON

22.45.11 #22 Text 0 File DVDR.cpp, Line 1600
Start write address at LBA 0
DVD high compatibility mode: Yes

22.45.11 #23 Text 0 File Cdrdrv.cpp, Line 7906
---- DVD Structure: Physical Format Information (00h) ----
Layer: 0, Address: 0 (0 h), AGID: 0; Length: 2050
Book Type: DVD-R (2), Part Version: 5
Disc Size: 120 mm, Maximum Rate: <not specified> (F h)
Number of Layers: 1, Track Path: Parallel Track Path (PTP), Layer Type: recordable
Linear Density: 0,267 um/bit, Track Density: 0,74 um/track
Starting Physical Sector Number of Data Area: 30000 h (DVD-ROM, DVD-R/-RW, DVD+R/+RW)
End Physical Sector Number of Data Area: 0 h
End Sector Number in Layer 0: 0 h
Data in Burst Cutting Area (BCA) does not exist
Media Specific:
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 - 00 00 00 00 00 00 00 00 ................

22.45.26 #24 Text 0 File Writer.cpp, Line 318
22:45:26.386 - SONY DVD RW DW-U50A : Queue again later (Intervall : 47msec)

22.47.01 #25 SCSI -1135 File Cdrdrv.cpp, Line 1415
SCSI Exec, HA 1, TA 0, LUN 0, buffer 0x089A0000
Status: 0x04 (0x01, SCSI_ERR)
HA-Status 0x00 (0x00, OK)
TA-Status 0x02 (0x01, SCSI_TASTATUS_CHKCOND)
Sense Key: 0x03 (KEY_MEDIUM_ERROR)
Sense Code: 0x0C
Sense Qual: 0x08
CDB Data: 0x2A 0x00 0x00 0x00 0x08 0xC0 0x00 0x00 0x20 0x00 0x00 0x00
Sense Data: 0xF1 0x00 0x03 0xFF 0xFD 0x00 0x00 0x12
0x00 0x00 0x00 0x00 0x0C 0x08

22.47.01 #26 CDR -1135 File Writer.cpp, Line 335
Write error

22.47.01 #27 Text 0 File ThreadedTransfer.cpp, Line 227
all writers idle, stopping conversion

22.47.02 #28 Text 0 File ThreadedTransfer.cpp, Line 221
conversion idle, stopping reader

22.47.02 #29 Text 0 File dlgbrnst.cpp, Line 1703
Set remaining time: 0:00,000 (0ms) -> OK

22.47.02 #30 Text 0 File dlgbrnst.cpp, Line 1703
Set remaining time: 0:00,000 (0ms) -> OK

22.47.02 #31 Phase 38 File dlgbrnst.cpp, Line 1843
Burn process failed at 1x (1.380 KB/s)


Existing drivers:
File 'Drivers\PXHELP20.SYS': Ver=2.02.42a, size=17184 bytes, created 21/10/2002 10.33.40 (Prassi/Veritas driver for win 2K)
File 'Drivers\atapi.sys': Ver=5.1.2600.1106 (xpsp1.020828-1920), size=86912 bytes, created 10/09/2002 14.00.00 (Adapter driver for rec)

Registry Keys:
HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinLogon\AllocateCDROMs : 0 (Security Option)

Thanks for help.