The trick was:
1. Re-generate public keys in moodle and mahara.
2. Erase mahara connection from moodle for the institution and do it again.
3. Reassign user's to new connection of the institution. In our case was easy because we have only one institution.
and it works... maybe there is a more short way, but this it worked for us.
PD: see you in La Rioja