I get the same error on the same field via VBO and Term merge:
An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: /batch?id=87&op=do StatusText: Service unavailable (with message) ResponseText: PDOException: SQLSTATE[21S01]: Insert value list does not match column list: 1136 Column count doesn't match value count at row 1: INSERT INTO {field_data_field_obligations} (entity_type, entity_id, revision_id, bundle, delta, language, field_obligations_url, field_obligations_title, field_obligations_attributes) 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_target, :db_insert_placeholder_8_rel, :db_insert_placeholder_8_class, :db_insert_placeholder_8_configurable_title, :db_insert_placeholder_8_title); Array ( [:db_insert_placeholder_0] => node [:db_insert_placeholder_1] => 2072 [:db_insert_placeholder_2] => 2107 [:db_insert_placeholder_3] => data [:db_insert_placeholder_4] => 0 [:db_insert_placeholder_5] => und [:db_insert_placeholder_6] => [:db_insert_placeholder_7] => [:db_insert_placeholder_8_target] => default [:db_insert_placeholder_8_rel] => [:db_insert_placeholder_8_class] => [:db_insert_placeholder_8_configurable_title] => 0 [:db_insert_placeholder_8_title] => ) in field_sql_storage_field_storage_write() (line 448 of /data/www/drupal7/modules/field/modules/field_sql_storage/field_sql_storage.module).
The final field listed "field_obligations_attributes" exists in the field_data_field_obligations table. I don't see where the 4 atribute fields are coming from (_target, _rel, _class, _title). The "field_obligations" field in field_config looks fine to me too - have type "link_field" and looks like other link_field fields that I have in this same entity.
I'd be happy to collect more information if someone could point me in the right direction?