Sorry, it didn't solve the probleme and I'm still stuck. My host disabled mod_sec on my moodle and mahara's urls but with no result on the ability to sso from moodle to mahara.
To bad I can't code. Actually I was wondering if someone with coding abilities couldn't offer an easier solution. I connected successfully my moodle to a Xerte on-line Toolkits install thanks to a moodle patch (this is how xerte developpers call it, but this is actually a Xerte patch). Xerte on-line toolkits is an online multimedia authoring tool and repository supposed to be only working with LDAP. The patch replaces 3 files in Xerte and points to Moodle config.php. All my moodle users access to xerte through a link and this automatically creates users in xerte. Would be so nice to have such a simple solution with mahara...
Cheers, Franck