kernel 2.6.17-gentoo-r8

[o_O]

Like, hi.

I have upgraded to the above kernel, but it's not being cool.

Everything was working fine on 2.6.15, except it didn't like my card reader, which is fixed in 2.6.17, so that's my reason for upgrading.

The actual problem is that the kernel can't mount my root partition (/dev/sda4), so it gives me a error:
[q=gentoo]Block device /dev/sda4 is not a valid root device[/q]
and then asks me to specify a root device.

For some reason, the drive mapping seems to have shifted along; I have two SATA hard drives in my box and what was previously /dev/sda is now /dev/sdb, etc.
I'm pretty sure it either has something to do with my grub.conf or SCSI support. I have tried compiling support for SCSI into the kernel and using modules. With both, if I try booting using /dev/sdb, it boots until it comes to mounting the partition /dev/sdb4, and then tells me
[q=gentoo]"Could not fix filesystem "[/q]
and I can either get into a shell for maintenance or reboot.
It appears to successfully load my SCSI modules though.

I'm booting from Grub using the following kernel section

title=Gentoo Linux (2.6.17-gentoo-r8)
root(hd0,2)
kernel /boot/kernel-genkernel-x86_64-2.6.17-gentoo-r8 root=/dev/ram0 init=linuxrc ramdisk=8192 real_root=/dev/sda4 udev video=vesafb:ywrap,mtrr vga=0x31B splash=silent,theme=emergence CONSOLE=/dev/tty1
initrd (hd0,1)/boot/initramfs-genkernel-x86_64-2.6.17-gentoo-r8

It's a bit of a long shot, but any ideas? I've had a bit of a search for similar problems, but nothing seems to have fixed it.