Modifying an erroneous visudo file and cannot get into sudo

I recently modified the visudo file and turns out I can't get into visudo mode at all. Worst is that in Ubuntu 12.04 we can't use "su" command or log in as "root"

Here is the tips, from here

Use pkexec command,

Just type "pkexec visudo"

And modify or restore back to the original settings.