Problem with AHC driver.

Hi...

I updated my system last night with make world/make kernel/mergemaster, and 
the new kernel doesn't seem to work.
It sits there for a while at "Waiting for SCSI devices to settle" and then 
gives the following message.

ahc0: Timedout SCB already complete.
Interrupts may not be functioning.
(probe1:ahc:0:1:0): SCB 0x8 - timed out

It then dumps the card state, which I can copy down if needed, but it'll have 
to be by hand, since I don't have a serial console.

An older kernel (May 7th 2003) works fine.

The controller is:
ahc0: <Adaptec 2940 Ultra SCSI adapter> port 0xd800-0xd8ff mem 
0xde000000-0xde000fff irq 15 at device 9.0 on pci0
aic7880: Ultra Wide Channel A, SCSI Id=7, 16/253 SCBs

The drives on the card are:
da0 at ahc0 bus 0 target 8 lun 0
da0: <IBM DCAS-34330W S65A> Fixed Direct Access SCSI-2 device 
da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit)
da0: 4134MB (8467200 512 byte sectors: 64H 32S/T 4134C)
and
cd0 at ahc0 bus 0 target 3 lun 0
cd0: < CD-R/RW RW7060S 1.50> Removable CD-ROM SCSI-2 device 
cd0: 3.300MB/s transfers

The cd-rw drive is external, if that makes any difference.
I'm pretty sure my cabling and termination are good, as I've been running in 
this setup for over a year now without any problems.
The motherboard is an ASUS P5A, with an AMD K6-2/500MHz processor.

Does anyone have a clue what's wrong, and/or how to fix it?
I'm happy to provide any debugging information requested, just tell me what 
you need and how to get it.

Thanks
 -Adam