This one seems to be a really famous problem for most folks in Ubuntu 9.10 Karmic Koala. So I had it too. The problem was on the initrd file. It is a kernel related file needed for booting. So i did a simple thing. I replaced initrd.img file of my kernel version with “initrd.lz” file from the Ubuntu LiveCD and edited my grub.cfg file (equivalent of menu.lst in older Ubuntu releases), to boot using initrd.