diff --git a/product/ERP5Form/MultiRelationField.py b/product/ERP5Form/MultiRelationField.py
index 4b46a7263a34f69b6854527eb373a0a0d1b7864d..73c8e0bb39be023da748fa1640d6d77453ace11c 100755
--- a/product/ERP5Form/MultiRelationField.py
+++ b/product/ERP5Form/MultiRelationField.py
@@ -411,7 +411,11 @@ class MultiRelationStringFieldValidator(Validator.LinesValidator,  RelationField
               if relation_uid not in (None, ''):
                 # A value has been defined by the user in  popup menu
                 if type(relation_uid) in (type([]), type(())): relation_uid = relation_uid[0]
-                related_object = portal_catalog.getObject(relation_uid)
+                try:
+                  related_object = portal_catalog.getObject(relation_uid)
+                except ValueError:
+                  # Catch the exception raised when the uid is a string
+                  related_object = None
                 if related_object is not None:
                   display_text = str(related_object.getProperty(catalog_index))
                 else:
diff --git a/product/ERP5Form/RelationField.py b/product/ERP5Form/RelationField.py
index 3f38b17212abd774b7b60679fb186c1f08ed460b..a6475d40f46d2a9b53a0906b18db41309e6a316a 100755
--- a/product/ERP5Form/RelationField.py
+++ b/product/ERP5Form/RelationField.py
@@ -350,7 +350,11 @@ class RelationStringFieldValidator(Validator.StringValidator):
           else:
             relation_uid = relation_uid[0]
 
-        related_object = portal_catalog.getObject(relation_uid)
+        try:
+          related_object = portal_catalog.getObject(relation_uid)
+        except ValueError:
+          # Catch the error raised when the uid is a string
+          related_object = None
         if related_object is not None:
           display_text = str(related_object.getProperty(catalog_index))
         else: