You mentioned in your first post that you were booting from the rescue CD. If this is what you're doing, why would you need to edit the GRUB menu to get into single user mode?
The rescue disk should automatically boot you into init level 3 with you drives unmounted, and let you run
fsck (or
tun2fs) as you wish.
What file system do you have on
/dev/sda6? (I had assumed that it was
/common because that was where it first error was reported.)
Are you using Logical Volume Management on your drives? I ask because
fsck will
completely destroy all logical volumes on a partition used by LVM if it is run on the raw partition. You can only run
fsck on the logical volumes listed under
/dev/mapper/Volume_group_name/Logical_Volume_Name after the logical volume is activated.
Are you sure that the "Enter" key actually worked? The boot may have continued because the timeout period expired.
I've only had the problem you describe when my keyboard cable was disconnected.
If your keyboard is connected, try pressing the "Escape" key (or Ctrl-[) to see if that gets GRUB's attention.