Nero buffer underrun

Hello.
Seems like i can burn any kind of discs, except audio discs in nero.
Everything starts normally, but then the buffer indicator begins falling and then it's full again; that happens like 3 or 4 times then the burning process fails.
i have no idea what it could be, a few days everything was alright.
Since then i haven't burned one single audio disc.
What could be causing the buffer problem?

Thanks in advance.

This is what i think is important in the log file:

23:13:07 #19 CDR -1106 File Writer.cpp, Line 311
Power calibration error

23:13:07 #20 Text 0 File ThreadedTransfer.cpp, Line 228
all writers idle, stopping conversion

23:13:07 #21 Text 0 File ThreadedTransfer.cpp, Line 222
conversion idle, stopping reader

23:13:08 #22 CDR -201 File WriterStatus.cpp, Line 200
Invalid write state
SAMSUNG CD-R/RW SW-212B\H1 T0

23:13:08 #23 TRANSFER -18 File WriterStatus.cpp, Line 200
Could not perform EndTrack

23:13:08 #24 Text 0 File Mmc.cpp, Line 15737
<SAMSUNG CD-R/RW SW-212B > start Close Session

23:13:08 #25 SCSI -1023 File Cdrdrv.cpp, Line 1176
SCSI Exec, HA 1, TA 0, LUN 0
Status: 0x04 (0x01, SCSI_ERR)
HA-Status 0x00 (0x00, OK)
TA-Status 0x02 (0x01, SCSI_TASTATUS_CHKCOND)
Sense Key: 0x05 (KEY_ILLEGAL_REQUEST)
Sense Code: 0x2C
Sense Qual: 0x00
CDB Data: 0x5B 0x01 0x02 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
Sense Data: 0x70 0x00 0x05 0x00 0x00 0x00 0x00 0x0A
0x00 0x00 0x00 0x00 0x2C 0x00

23:13:08 #26 CDR -1023 File WriterStatus.cpp, Line 249
Command sequence error

23:13:08 #27 TRANSFER -19 File WriterStatus.cpp, Line 249
Could not perform Fixation

23:13:08 #28 Text 0 File WriterStatus.cpp, Line 258
falling back to disc fixation

23:13:08 #29 Phase 38 File dlgbrnst.cpp, Line 1832
Burn process failed at 12x (1.800 KB/s)