In the event that you have tried downgrading from Ubuntu 11.10 to Ubuntu 11.04 using an Ubuntu 11.04 CD / DVD and now have a system failing to boot the following steps should allow you to reinstall Ubuntu 11.04 and have a working system.
1) Boot and 11.04 CD
2) Choose Try Ubuntu
3) Download "Install downgrade patch" from this bug report
4) Open a terminal
5) Execute "sudo patch /usr/share/ubiquity/install.py < ubiquity-downgrade-patch.py" in the terminal
6) Run the installer from the desktop
7) After the install completes reboot the system
8) In the grub menu from the installed system choose "Previous Linux versions"
9) Select the first 2.6.38 kernel version
Now you should be running 11.04 and have access to all your documents.
In the event that you have tried downgrading from Ubuntu 11.10 to Ubuntu 11.04 using an Ubuntu 11.04 CD / DVD and now have a system failing to boot the following steps should allow you to reinstall Ubuntu 11.04 and have a working system.
1) Boot and 11.04 CD ubiquity/ install. py < ubiquity- downgrade- patch.py" in the terminal
2) Choose Try Ubuntu
3) Download "Install downgrade patch" from this bug report
4) Open a terminal
5) Execute "sudo patch /usr/share/
6) Run the installer from the desktop
7) After the install completes reboot the system
8) In the grub menu from the installed system choose "Previous Linux versions"
9) Select the first 2.6.38 kernel version
Now you should be running 11.04 and have access to all your documents.