Error 17 is "can't mount the selected partition. If this is the first meesage then the installer has told Grub the wrong partition to pick up the kernel.
If a Linux has bugs its installer normally has the lion's share.
We need the output of terminal "fdisk -l" as well as the /boot/grub/menu.lst to advise further.
In the mean time you can gain access to Ubuntu by any Live CD (Task H1 and H2 of the last link of my signature refers)