Obfuscation not doin' nothing

I am trying to obfuscate my project, and enabling the setting produces no results what so ever, no errors or messages at all.
<target name="-post-compile">
<fileset dir="${build.classes.dir}"/>

To my build gives me the error:
Problem: failed to create task or type obfuscate
Cause: The name is undefined.
Action: Check the spelling.
Action: Check that any custom tasks/types have been declared.
Action: Check that any <presetdef>/<macrodef> declarations have taken place.

Any ideas?

The obfuscation checkbox in the project settings works fine for me?

I am working in Centos6.
Would that cause any changes?

If centos randomly deletes lines from config files or doesn’t let you write to random files then yes.