Let's solve this once and for all

The well known error: CW Image Optimizer requires littleutils. You are missing: opt-png, opt-jpg, opt-gif.
I have Ubuntu 12.04 64bit, nginx, php5-fpm, mysql, phpmyadmin, fail2ban, postfix, littleutils 1.0.29.
I’ve installed littleutils as instructed.
Installation was successful, the only error i saw was:
gifsicle utility missing: skipping opt-gif
pngcrush utility missing: skipping opt-png

Although gifsicle and pngcrush are installed:
libjpeg-progs is already the newest version.
libpng12-0 is already the newest version.
libpng12-dev is already the newest version.
gifsicle is already the newest version.
lzip is already the newest version.
p7zip-full is already the newest version.
pngcrush is already the newest version.

Symbolic links are there:
ln: failed to create symbolic link `/usr/bin/opt-jpg’: File exists

Trying to opt-jpg via ssh fails:
opt-jpg warning: http://static.mujo.ro/2013/07/iulie-2013-concurs.jpg is not a writeable non-directory file

Media Gallery folders have 775, files 664.

Clicking “skip littleutils check” throws “Bad response from optimizer” error.

So, what is the problem?

Could it be a user issue? On a previous server processes ran as www-data (CW plugin worked) but now are running as “username” (CW plugin not working).

How can this be solved?

Thank you.

http://wordpress.org/extend/plugins/cw-image-optimizer/