diff --git a/address.py b/address.py
index 3017b89fb8..a1b6c0b6c6 100644
--- a/address.py
+++ b/address.py
@@ -45,8 +45,8 @@ class Address(ModelSQL, ModelView):
         cls._order.insert(0, ('party', 'ASC'))
         cls._order.insert(1, ('sequence', 'ASC'))
         cls._error_messages.update({
-            'write_party': 'You can not modify the party of an address!',
-            })
+                'write_party': 'You can not modify the party of address "%s".',
+                })
 
     @classmethod
     def __register__(cls, module_name):
@@ -114,7 +114,7 @@ class Address(ModelSQL, ModelView):
         if 'party' in vals:
             for address in addresses:
                 if address.party.id != vals['party']:
-                    cls.raise_user_error('write_party')
+                    cls.raise_user_error('write_party', (address.rec_name,))
         super(Address, cls).write(addresses, vals)
 
     def on_change_country(self):
diff --git a/category.py b/category.py
index 8ec6fe5170..267c12e29c 100644
--- a/category.py
+++ b/category.py
@@ -29,26 +29,28 @@ class Category(ModelSQL, ModelView):
         super(Category, cls).__setup__()
         cls._sql_constraints = [
             ('name_parent_uniq', 'UNIQUE(name, parent)',
-                'The name of a party category must be unique by parent!'),
-        ]
-        cls._constraints += [
-            ('check_recursion', 'recursive_categories'),
-            ('check_name', 'wrong_name'),
-        ]
+                'The name of a party category must be unique by parent.'),
+            ]
         cls._error_messages.update({
-            'recursive_categories': 'You can not create recursive categories!',
-            'wrong_name': 'You can not use "%s" in name field!' % SEPARATOR,
-        })
+                'wrong_name': ('Invalid category name "%%s": You can not use '
+                    '"%s" in name field.' % SEPARATOR),
+                })
         cls._order.insert(1, ('name', 'ASC'))
 
     @staticmethod
     def default_active():
         return True
 
+    @classmethod
+    def validate(cls, categories):
+        super(Category, cls).validate(categories)
+        cls.check_recursion(categories, rec_name='name')
+        for category in categories:
+            category.check_name()
+
     def check_name(self):
         if SEPARATOR in self.name:
-            return False
-        return True
+            self.raise_user_error('wrong_name', (category.name,))
 
     def get_rec_name(self, name):
         if self.parent:
diff --git a/category.xml b/category.xml
index 71e9f471bf..b1706de7eb 100644
--- a/category.xml
+++ b/category.xml
@@ -97,5 +97,14 @@ this repository contains the full copyright notices and license terms. -->
             <field name="perm_delete" eval="True"/>
         </record>
 
+        <record model="ir.translation" id="party_category_recursion_error">
+            <field name="name">party.category</field>
+            <field name="lang">en_US</field>
+            <field name="type">error</field>
+            <field name="src">recursion_error</field>
+            <field name="value">Recursion error: Party Category "%(rec_name)s" with parent "%(parent_rec_name)s" was configured as ancestor of itself.</field>
+            <field name="module">party</field>
+            <field name="fuzzy" eval="False"/>
+        </record>
     </data>
 </tryton>
diff --git a/contact_mechanism.py b/contact_mechanism.py
index aa1c4f5da4..ed2f981c94 100644
--- a/contact_mechanism.py
+++ b/contact_mechanism.py
@@ -86,8 +86,8 @@ class ContactMechanism(ModelSQL, ModelView):
         cls._order.insert(0, ('party', 'ASC'))
         cls._order.insert(1, ('sequence', 'ASC'))
         cls._error_messages.update({
-                'write_party': ('You can not modify the party of '
-                    'a contact mechanism!'),
+                'write_party': ('You can not modify the party of contact '
+                    'mechanism "%s".'),
                 })
 
     @classmethod
@@ -171,5 +171,5 @@ class ContactMechanism(ModelSQL, ModelView):
         if 'party' in vals:
             for mechanism in mechanisms:
                 if mechanism.party.id != vals['party']:
-                    cls.raise_user_error('write_party')
+                    cls.raise_user_error('write_party', (mechanism.rec_name,))
         super(ContactMechanism, cls).write(mechanisms, vals)
diff --git a/party.py b/party.py
index f5379f2be5..4444183166 100644
--- a/party.py
+++ b/party.py
@@ -77,14 +77,12 @@ class Party(ModelSQL, ModelView):
         super(Party, cls).__setup__()
         cls._sql_constraints = [
             ('code_uniq', 'UNIQUE(code)',
-             'The code of the party must be unique!')
-        ]
-        cls._constraints += [
-            ('check_vat', 'invalid_vat'),
+             'The code of the party must be unique.')
         ]
         cls._error_messages.update({
-            'invalid_vat': 'Invalid VAT number!',
-        })
+                'invalid_vat': ('Invalid VAT number "%(vat)s" on party '
+                    '"%(party)s".'),
+                })
         cls._order.insert(0, ('name', 'ASC'))
 
     @staticmethod
@@ -219,6 +217,12 @@ class Party(ModelSQL, ModelView):
                 return address
         return default_address
 
+    @classmethod
+    def validate(cls, parties):
+        super(Party, cls).validate(parties)
+        for party in parties:
+            party.check_vat()
+
     def check_vat(self):
         '''
         Check the VAT number depending of the country.
@@ -241,8 +245,10 @@ class Party(ModelSQL, ModelView):
                     'vat_number': vat_number,
                     })
             else:
-                return False
-        return True
+                self.raise_user_error('invalid_vat', {
+                        'vat': vat_number,
+                        'party': party.rec_name,
+                        })
 
 
 class PartyCategory(ModelSQL):