I already make it 777.
Anyway, i solved it by making a little modification on my jython custom script at the beginning of the script like this:
sys.path.append("/opt/gluu/jetty/oxauth/lib/ext/testing_lib.jar") # -> Because it is located at /opt/gluu/jetty/oxauth/lib/ext
. . .
import com.fnsv.testing as TestLib;
Now I am facing another error, but not related to this ticket
Thanks for your response