The Facebook login feature works when a user has previously set up an account on my site. However, when I try to register a new user I get this error:

PDOException: SQLSTATE[HY000]: General error: 1364 Field 'signature' doesn't have a default value: INSERT INTO {users} (uid, name, mail, created, status, timezone, init, data) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7); Array ( [:db_insert_placeholder_0] => 197 [:db_insert_placeholder_1] =>

The signature refers to a field that was created from the signature module.
Site is called motoatx.com.

Thanks for any help!