Display useful error message if target proxy of field does not exist.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@16316 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/Form.py

@@ -780,7 +780,10 @@ class ERP5Form(ZMIForm, ZopePageTemplate):
 # utility function
 def get_field_meta_type_and_proxy_flag(field):
     if field.meta_type=='ProxyField':
-        return field.getRecursiveTemplateField().meta_type, True
+        try:
+            return field.getRecursiveTemplateField().meta_type, True
+        except AttributeError:
+            raise AttributeError, 'The proxy target of %s field does not exists. Please check the field setting.' % field.getId()
     else:
         return field.meta_type, False