Got this error while upgrading from Ubuntu 10.10 to 11.04
The disc drive for / is not ready yet or not present. Continue to wait, press S to skip or M for manual recovery.
Searched for solution and found this Ubuntu bug https://bugs.launchpad.net/ubuntu/+source/udev/+bug/753853
Solution given was do run command
sudo apt-get install -f
Reason given was
Broken branding-ubuntu package was causing apt to stop prematurely leaving the system in an inconsistent state.