Another test before I make holidays (please don't close this thread, I am back at Sep.8th).

booting with
knoppix testcd
...
some time later
Starting X11...scsi0: ERROR on channel 0, id 0, lun 0, CDB: Request Sense 00 00 00 40 00
Info fld=0x1b53f, Current sd0b:00: sense key Medium Error
Additional sense indicates Random positioning error
I/O error: dev 0b:00, sector 447740
cloop: Read error at pos 227676160 in file /cdrom/KNOPPIX/KNOPPIX, 20197 bytes lost.
cloop: error -5 uncompressing block 9742 65536/65536/27915/0 227668442-227696357
end_request: I/O error dev f00:00 (cloop), sector 1246992
...
scsi : aborting command due to timeout : pid 11543, scsi0, channel 0, id 0, lun 0 Read (10) 00 00 01
...
hdc: irq timeout: status 0xd0 { busy }
hdc: ATAPI reset complete
hdc: irq timeout: status 0xd0 { busy }
hdc: ATAPI reset complete
hdc: irq timeout: status 0xd0 { busy }
hdc: ATAPI reset complete
scsi0 channel 0: resetting for second half of retries.
SCSI bus is being reset for host 0 channel 0
kernel BUG at ide-scsi.c:561!
invalid operand: 0000
autofs4 nls_iso8859-1 ntfs xirc2ps_cs serial hisax isdn slhc ds i82365 pcmcia_core apm rtc cloop
CPU: 0
EIP: 0010:[<c01cb085>] Not tainted
EFLAGS: 00010282
eax: c1068c60 ebx: c0331e44 ecx: 0088f2c0 edx: c105d540
esi: c0331e44 edi: c0ff74f0 ebp: c06e0800 esp: c02c1e7c

ds: 0018 es: 0018 ss: 0018
Process swapper (pid: 0 stackpage=c02c1000)