How to fix boot failure due to incorrect fstab?

It seems that I've found a solution:

• at the grub prompt, hit a to append options
• add init=/bin/bash to the end of the kernel command line and press enter

The system will boot to a prompt like 'bash-3.2#' enter the following commands at the prompt

• mount -o remount,rw /
• vim /etc/fstab

edit the fstab file commenting the errors by adding a # at the begining of each problematic line, save the file

• reboot by pressing CTRL+ALT+DEL

How about removing the entry, creating a snapshot and then trying to change your /etc/fstab so you have a working snapshot you can roll back to?

According to the manpage mount.cifs you can also specify a password via password=arg. Also, according to that manpage there is no argument username=arg but instead user=arg. But it might be different on your system, better check your manpage for the correct argument names.