Please help me:

[Gábor Iglói]

I've experienced with vmware and executed the "sudo usermod -G disk
gabor" command to add my default user to the disk group (for allowing
gabor to direct access disk drives). One thing is that this didn't
work but unfortunately I have managed to mess up gabor's ability to
use the sudo method. After that every sudo attemp with this user gives
me the following error:

gabor is not in the sudoers file.  This incident will be reported.

(fortunately I have noticed the sudo problem in time and managed to
activate my root account temporarily)

I don't think I messed up my sudoers file as I didn't do anything with
it, but here is my current sudoers:

root at ubuntu:~ # cat /etc/sudoers
# /etc/sudoers
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the man page for details on how to write a sudoers file.
#

# Host alias specification
# User alias specification
# Cmnd alias specification
# Defaults

Defaults        !lecture,tty_tickets,!fqdn

# User privilege specification
root    ALL=(ALL) ALL

# Members of the admin group may gain root privileges
%admin  ALL=(ALL) ALL

I also tried to reset gabor's group with the command "usermod -G users
gabor" but this didn't help - as I don't know the default group
settings for Hoary.

Anybody can help me regain the sudo ability?
Thanks...