I'm afraid this is no longer possible in 1.6.x. With the new multi-enrol environment, internal enrolment is always on (in fact, you can't disable it unless you edit the code).
Mostafa, which exact version of Moodle are you running? Please paste the contents of ../moodle/version.php here.
Saludos. Iñaki.
Installing and upgrading help
is the 1.54 version the best one?
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