Suite MYSQL 2005 & Diagramme

Bonjour,
j'ai crée le diagramme de mes tables mais a la fin un MSG d'erreur s'est apparut :
'Utilisateur' table saved successfully
'Service' table saved successfully
'Modele' table saved successfully
'Materiel' table saved successfully
'Marque' table saved successfully
'DetailMateriel' table
- Unable to create relationship 'FK_DetailMateriel_Service'.
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_DetailMateriel_Service". The conflict occurred in database "ParcInfo", table "dbo.Service", column 'CodeSer'.


cé koi le pb ???
a l'aidddddddde