Intel 6300ESB SATA150 cannot find disk or boot under 6.3

[Greg Satz]

I have a DELL PE750 that boots fine under 6.1 but cannot boot 6.3. It  
appears that the SATA controller cannot initialize ata1 under 6.3.  
6.3 has no problem initializing ata0. My CDROM is on ata0 and the  
disk is on ata1. Here is the relevant portions of the verbose output:

6.3:

isab0: <PCI-ISA bridge> at device 31.0 on pci0
isa0: <ISA bus> on isab0
atapci0: <Intel 6300ESB SATA150 controller> port  
0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0xfea0-0xfeaf at device 31.2 on pci0
atapci0: Reserved 0x10 bytes for rid 0x20 type 4 at 0xfea0
ata0: <ATA channel 0> on atapci0
atapci0: Reserved 0x8 bytes for rid 0x10 type 4 at 0x1f0
atapci0: Reserved 0x1 bytes for rid 0x14 type 4 at 0x3f6
ata0: reset tp1 mask=03 ostat0=50 ostat1=00
ata0: stat0=0x00 err=0x01 lsb=0x14 msb=0xeb
ata0: stat1=0x00 err=0x00 lsb=0x00 msb=0x00
ata0: reset tp2 stat0=00 stat1=00 devices=0x4<ATAPI_MASTER>
ioapic0: routing intpin 14 (ISA IRQ 14) to vector 53
ata0: [MPSAFE]
ata1: <ATA channel 1> on atapci0
atapci0: Reserved 0x8 bytes for rid 0x18 type 4 at 0x170
atapci0: Reserved 0x1 bytes for rid 0x1c type 4 at 0x376
ata1: reset tp1 mask=03 ostat0=80 ostat1=80
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
...
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: stat0=0x80 err=0xff lsb=0xff msb=0xff
ata1: reset tp2 stat0=80 stat1=80 devices=0x0
ioapic0: routing intpin 15 (ISA IRQ 15) to vector 54
ata1: [MPSAFE]

6.1:

isab0: <PCI-ISA bridge> at device 31.0 on pci0
isa0: <ISA bus> on isab0
atapci0: <Intel 6300ESB SATA150 controller> port  
0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0xfea0-0xfeaf at device 31.2 on pci0
atapci0: Reserved 0x10 bytes for rid 0x20 type 4 at 0xfea0
ata0: <ATA channel 0> on atapci0
atapci0: Reserved 0x8 bytes for rid 0x10 type 4 at 0x1f0
atapci0: Reserved 0x1 bytes for rid 0x14 type 4 at 0x3f6
ata0: reset tp1 mask=03 ostat0=50 ostat1=00
ata0: stat0=0x00 err=0x01 lsb=0x14 msb=0xeb
ata0: stat1=0x00 err=0x00 lsb=0x00 msb=0x00
ata0: reset tp2 stat0=00 stat1=00 devices=0x4<ATAPI_MASTER>
ioapic0: routing intpin 14 (ISA IRQ 14) to vector 53
ata0: [MPSAFE]
ata1: <ATA channel 1> on atapci0
atapci0: Reserved 0x8 bytes for rid 0x18 type 4 at 0x170
atapci0: Reserved 0x1 bytes for rid 0x1c type 4 at 0x376
ata1: reset tp1 mask=03 ostat0=50 ostat1=00
ata1: stat0=0xd0 err=0x01 lsb=0x00 msb=0x00
ata1: stat0=0x50 err=0x01 lsb=0x00 msb=0x00
ata1: stat1=0x00 err=0x01 lsb=0x00 msb=0x00
ata1: reset tp2 stat0=50 stat1=00 devices=0x1<ATA_MASTER>
ioapic0: routing intpin 15 (ISA IRQ 15) to vector 54
ata1: [MPSAFE]

I have the full verbose logs from both boots but didn't want to bomb  
the mailing list if this was something simple. Any clues appreciated.

Thanks,
Greg