Si por error no se pueden asociar elementos en el plugin de Servicios ITIL de GLPI, hay que corregir la PRIMARY KEY de esta tabla :

ALTER TABLE glpi_plugin_services_services_items MODIFY COLUMN id INT AUTO_INCREMENT;
 
mysql> DESC glpi_plugin_services_services_items ;
+-----------------------------+--------------+------+-----+---------+----------------+
| FIELD                       | TYPE         | NULL | KEY | DEFAULT | Extra          |
+-----------------------------+--------------+------+-----+---------+----------------+
| id                          | INT(11)      | NO   | PRI | NULL    | AUTO_INCREMENT |
| plugin_services_services_id | INT(11)      | NO   | MUL | 0       |                |
| items_id                    | INT(11)      | NO   | MUL | 0       |                |
| itemtype                    | VARCHAR(100) | NO   | MUL | NULL    |                |
+-----------------------------+--------------+------+-----+---------+----------------+
4 ROWS IN SET (0.00 sec)