Fedora Users — mounted data dvds not read correctly

I recently became aware that there is something going wrong when I mount data dvds on my fedora core 4 system. I became aware of this using a data dvd rom that contains some software from Sun. I have tested that the dvd is ok by using another system. The symptom is that when I mount this dvd and try to compute checksums of files on it I get a different random answer on each mount. There are no signs of trouble as the system boots -- here is the relevant section of /var/log/dmesg:

ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
ICH6: IDE controller at PCI slot 0000:00:1f.1
ACPI: PCI Interrupt 0000:00:1f.1[A] -> GSI 18 (level, low) -> IRQ 193
ICH6: chipset revision 3
ICH6: not 100% native mode: will probe irqs later
ide0: BM-DMA at 0xffa0-0xffa7, BIOS settings: hda:DMA, hdb:DMA
Probing IDE interface ide0...
hda: HP DVD Writer 640b, ATAPI CD/DVD-ROM drive
hdb: ASUS CD-S480/AH, ATAPI CD/DVD-ROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
Probing IDE interface ide1...
hda: ATAPI 40X DVD-ROM DVD-R CD-R/RW drive, 2048kB Cache, UDMA(33)
Uniform CD-ROM driver Revision: 3.20
hdb: ATAPI 48X CD-ROM drive, 128kB Cache, UDMA(33)

If it matters, the system is an hp pavilions desktop model a820n.

As far as I can see, video dvds play fine on the same dvd drive.

There are no messages produced to either dmesg or to /var/log/messages when mounting or reading files from the dvd.

I am running the latest fedora 4 kernel: kernel-smp-2.6.16-1.2108_FC4. The problem also occurs with an older fedora 4 kernel: kernel-smp-2.6.15-1.1833_FC4.

Can anyone suggest anything I can do to work around this problem, or to track down where it occurs?

Thanks,

Steve Schwarz