Error on og_mandatory_groups_by_role

When I go to "/drupal/admin/og/og_multiple_mandatory_groups_by_role/groups" and try to delete some group, there's the following error:

* warning: Illegal offset type in unset in /var/www/drupal/modules/og_multiple_mandatory_groups_by_role/og_multiple_mandatory_groups_by_role.module on line 783.
* warning: Illegal offset type in unset in /var/www/drupal/modules/og_multiple_mandatory_groups_by_role/og_multiple_mandatory_groups_by_role.module on line 783.

I've open a issue, but I'll appreciate if anyone knows the solution.

Thanks!