Sudo fails even with seeming correct permissions?

Question

When I try to sudo from Terminal, I get:
media:~ frank$ sudo su -
sudo: unable to stat /etc/sudoers: Permission denied
sudo: no valid sudoers sources found, quitting
However, I can cat /etc/sudoers and see the content of the file. I'm a member of the admin group.
Thanks in advance, additional info available if it will help!

Answer 1

Valid is not the same as a file exists.  The /etc/sudoers file needs to be correct format and permissions.
/bin/ls -leO@ /etc/sudoers
-r--r-----  1 root  wheel  compressed 1275 Oct 31 22:54 /etc/sudoers
Have you edited /etc/sudoers ?
What tool did you use to modify /etc/sudoers ?
You are suppose to use /usr/sbin/visudo to edit the /etc/sudoers file which will validate the results before saving the updated version.  See "man visudo".
While I am still using Mavericks, chances are the /etc/sudoers file still looks the same, so here is what my unmodified /etc/sudoers file looks like:
# 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