DD Problem Dumping a UDF-Formatted CD

Sir/Madam,

I'm having problems getting dd to dump the abovementioned CD, whether 
it's a bug I don't know. There is a surprisingly large number of 
"input/output errors", at strangely regular intervals.

The dd command and the output, summarized, follow:

[drj:Development/DICOM/CR-EchoCD-rawwrites] jonathan# dd conv=noerror \
	if=/dev/disk1s0 of=bennyd.20040402.diskdump1.txt

dd: reading `/dev/disk1s0': Input/output error
1440+0 records in
1440+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
1984+0 records in
1984+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
2136+0 records in
2136+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
5352+0 records in
5352+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
8568+0 records in
8568+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
11784+0 records in
11784+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
15000+0 records in
15000+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
18216+0 records in
18216+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
21432+0 records in
21432+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
24648+0 records in
24648+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
27864+0 records in
27864+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
31080+0 records in
31080+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
32520+0 records in
32520+0 records out
(3 lines repeated 31 additional times)
dd: reading `/dev/disk1s0': Input/output error
34248+0 records in
34248+0 records out
(3 lines repeated 63 additional times)
dd: reading `/dev/disk1s0': Input/output error
35240+0 records in
35240+0 records out
(3 lines repeated 7 additional times)
35240+0 records in
35240+0 records out


Here's what the application "disktype" has to say about the CD:

[drj:~] jonathan% disktype /dev/disk1

--- /dev/disk1
Block device, size 20.03 MiB (21008064 bytes)
disktype: Data read failed at position 21004288: Input/output error
Raw CD image, Mode 2, assuming Form 1
disktype: Data read failed at position 21000192: Input/output error
UDF file system
   Sector size 2048 bytes
   Volume name "Benny"
   UDF version 1.50
ISO9660 file system
   Volume name "Benny"
   Application "CDUDF File System - Adaptec Inc"
   Data size 16.94 MiB (17762304 bytes, 8673 blocks of 2 KiB)
   Joliet extension, volume name "Benny"

[drj:~] jonathan% disktype /dev/disk1s0

--- /dev/disk1s0
Block device, size 17.45 MiB (18292736 bytes)
disktype: Data read failed at position 18288640: Input/output error
UDF file system
   Sector size 2048 bytes
   Volume name "Benny"
   UDF version 1.50
ISO9660 file system
   Volume name "Benny"
   Application "CDUDF File System - Adaptec Inc"
   Data size 16.94 MiB (17762304 bytes, 8673 blocks of 2 KiB)
   Joliet extension, volume name "Benny"

Are you aware of any kind of problem that might cause such singular "errors"?

TIA,

Jonathan