Hosed Intel DP35DP Centos 5.3 upgrade

[jamestastic]

I have an intel DP35DP motherboard - ICH9 southbridge - set to AHCI mode. Working fine under 5.2.
Yesterday I updated to centos 5.3, and got kernel 2.6.18-128.1.16 and now it can't boot. It hangs trying to read sata1 with DRDY errors and exceptions.
So then I installed 5.3 from a DVD onto a new drive, and got kernel 2.6.18-128. This worked, most of the time, but occasionally gave me this error. I then updated my BIOS, and the error went away.
Then I updated this new working drive to the latest kernel (yum update again) and got kernel 2.6.18-128.1.16, and now it wont boot again, with the same message.

ata1: failed to read log page 10h (errno=-5)
ata1.00 exception Emask 0x1 SAct 0x1 SErr 0x0 action 0x0
ata1.00: irq_stat 0x40000008
ata1.00: cmd 60/08:00:61:4b:38/00:00:3a:00:00/40 tag 0 ncq 4096 in
ata1.00: status: { DRDY }
ata1.00: revalidation failed (errno=-2)
ata1.00: revalidation failed (errno=-2)
ata1.00: revalidation failed (errno=-2)
Buffer I/O error on device dsa3, logical block 119973392
more of these
mount: count not find filesystem '/dev/root'
etc.

I have read a lot about ahci problems, but I have yet to find a fix.

[jamestastic]

Well, I tried moving the ahci.ko insmod to the top of the init script. No go.
I tried acpi=off, pci=nomsi, irqpoll, etc. All no go.
I noticed that the second drive I used had its 1.5Gb jumper set - pulled it off - still no go.
Finally I've switched the mobo to IDE/Native, and then IDE/legacy. Not only will it not boot in this state, but now the install DVD can't see it (same errors) so I can't even install in legacy mode. Sweet.

Totally wierd. It booted after installing 5.3 from scratch and I used that drive to try to resurrect the other. Then, as a test, I updated to the latest kernel, and now that drive is unbootable too: and its unbootable using the original 5.3 kernel that is still there.

[jamestastic]

I hung my drive off an old Promise SATA TX4 and it boots.

Jamie