sudo: /etc/sudoers is owned by uid 501, should be 0
sudo: no valid sudoers sources found, quitting

mount -uw /
chown root:wheel /etc/sudoers
chmod 440 /etc/sudoers
reboot

# sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
# Failure to use 'visudo' may result in syntax or file permission errors
# that prevent sudo from running.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# Host alias specification

# User alias specification

# Cmnd alias specification

# Defaults specification
Defaults    env_reset
Defaults    env_keep += "BLOCKSIZE"
Defaults    env_keep += "COLORFGBG COLORTERM"
Defaults    env_keep += "__CF_USER_TEXT_ENCODING"
Defaults    env_keep += "CHARSET LANG LANGUAGE LC_ALL LC_COLLATE LC_CTYPE"
Defaults    env_keep += "LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME"
Defaults    env_keep += "LINES COLUMNS"
Defaults    env_keep += "LSCOLORS"
Defaults    env_keep += "SSH_AUTH_SOCK"
Defaults    env_keep += "TZ"
Defaults    env_keep += "DISPLAY XAUTHORIZATION XAUTHORITY"
Defaults    env_keep += "EDITOR VISUAL"
Defaults    env_keep += "HOME MAIL"

# Runas alias specification

# User privilege specification
root    ALL=(ALL) ALL
%admin  ALL=(ALL) ALL

# Uncomment to allow people in group wheel to run all commands
# %wheel    ALL=(ALL) ALL

# Same thing without a password
# %wheel    ALL=(ALL) NOPASSWD: ALL

# Samples
# %users  ALL=/sbin/mount /cdrom,/sbin/umount /cdrom
# %users  localhost=/sbin/shutdown -h now

machine:~ user$ ls /private/etc/sudoers
-r--r-----  1 root  wheel  1275 13 Jun  2012 /private/etc/sudoers

/etc/sudoers

total 0
drwxr-xr-x  2 501  0   68 Oct 23 23:56 yourusername
drwx------  3 501  0  102 Nov 24 00:57 ts

total 0
drwx--x--x   4 yourusername   wheel   136 Oct 23 23:56 .
drwxr-xr-x  80 yourusername   wheel  2720 Nov 24 01:55 ..
drwxr-xr-x   2 root  wheel    68 Oct 23 23:56 yourusername
drwx------   3 root  wheel   102 Nov 24 00:57 ts

total 0
drwx--x--x   4 root  wheel   136 Oct 23 23:56 .
drwxr-xr-x  80 root  wheel  2720 Nov 24 01:55 ..
drwxr-xr-x   2 root  wheel    68 Oct 23 23:56 yourusername
drwx------   3 root  wheel   102 Nov 24 00:57 ts

total 0
drwxr-xr-x  2 0  0   68 Oct 23 23:56 dan
drwx------  3 0  0  102 Nov 24 00:57 ts
UID is now set to 0 and not 501.

-r--r-----  1 501  0  1563 Nov 14 17:53 /private/etc/sudoers

-r--r-----  1 0  0  1563 Nov 14 17:53 /private/etc/sudoers

sudo su
sudo chown -R root:wheel /var/db/sudo/ts/