Supporter subscribe stuck in loop

Hello,
When a new user tries to subscribe on supporter he goes from

domain/subsite/wp-admin/supporter.php to
domain/subsite/wp-admin/supporter.php#supporter-php
or domain/subsite/wp-admin/index.php#supporter-php
over and over and he cannot subscribe

Multisite 3.1.2
Product theme
Membership plugin deactivated