Index: __init__.py
===================================================================
--- __init__.py	(.../http://code.djangoproject.com/svn/django/trunk/django/db/models/fields/__init__.py)	(revision 6535)
+++ __init__.py	(.../__init__.py)	(working copy)
@@ -468,7 +468,7 @@
             if self.null:
                 return value
             else:
-                raise validators.ValidationError, ugettext_lazy("This field cannot be null.")
+                raise validators.ValidationError, ugettext_lazy("The field '%s' cannot be null." %  self.name)
         return smart_unicode(value)
 
     def formfield(self, **kwargs):