This might be a bit late as I imagine many have just moved on to 10.04 but for those of you that haven't and any others who just want to fix 9.10 please read on...
I too encountered this error on 9.10 after a kernel upgrade (to -19) and I foolishly removed the old kernels without testing. Mine is NOT a Wubi install either (its dual boot XP with 9.10 installed to a ext4 partition).
Not sure if it'll work for others but I found that for some reason Grub2 gets it wrong. In the .cfg it counts the first partition as 0 rather than 1 so its one out.
but Linux is on sda7 so I changed it toCode:set root=(hd0,6)
and it booted fine!Code:set root=(hd0,7)
I edited my /boot/grub/grub.cfg from a live cd but you should only need to edit the boot entry in grub itself (while booting). Once your desktop loads, update the kernel (I used Synaptic but obviously CLI or Update Manager are fine) and you should be good to go. Installing a new kernel will trigger grub to update (and fix) grub.cfg.
Worked for me anyway.