error when attempting inline registration

I have been using Inline Registration fine on a D6 site.

I have tried on three D7 sites and each time I try to create content, as an anonymous user, with inline registration, the following error:

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key 2: INSERT INTO {users} (uid, name, pass, mail, signature, created, status, language, picture, 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, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10); Array ( [:db_insert_placeholder_0] => 3 [:db_insert_placeholder_1] => [:db_insert_placeholder_2] => $S$DEKfebw0ftza6RAP6DDVGJGV6h4ut2ppCb3jej1DWfKhVSUtKKWH [:db_insert_placeholder_3] => erich@dmicapital.com [:db_insert_placeholder_4] => Array [:db_insert_placeholder_5] => 1316631920 [:db_insert_placeholder_6] => 1 [:db_insert_placeholder_7] => und [:db_insert_placeholder_8] => 0 [:db_insert_placeholder_9] => erich@dmicapital.com [:db_insert_placeholder_10] => a:1:{s:7:"contact";i:1;} ) in drupal_write_record() (line 6868 of /includes/common.inc).

I tried 3 different sites to see if their might be a module conflict or conflct with certain entities / fields. I tried with a basic Article and same error.