User defined defaults gives error on Advance Product in Advance Invoice

[gobi]

I created a user define defaults as in attached.

Named:product_id
Model Name:sale.advance.payment.inv
Default Value:31

When I try to create advance invoice it give error.

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OpenERP Server Error
Client Traceback (most recent call last):
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/common/http.py", line 180, in dispatch
    response["result"] = method(controller, self, **self.params)
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/controllers/main.py", line 1044, in call
    return self.call_common(req, model, method, args, domain_id, context_id)
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/controllers/main.py", line 996, in call_common
    return self._call_kw(req, model, method, args, {})
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/controllers/main.py", line 1010, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/common/openerplib/main.py", line 250, in proxy
    args, kw)
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/common/openerplib/main.py", line 117, in proxy
    result = self.connector.send(self.service_name, method, *args)
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/common/http.py", line 608, in send
    raise xmlrpclib.Fault(openerp.tools.exception_to_unicode(e), formatted_info)

Server Traceback (most recent call last):
  File "/home/sysadmin/openerp-web/branches/6.1/addons/web/common/http.py", line 593, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/netsvc.py", line 360, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/service/web_services.py", line 586, in dispatch
    res = fn(db, uid, *params)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/osv/osv.py", line 167, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/osv/osv.py", line 121, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/osv/osv.py", line 176, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/osv/osv.py", line 164, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/sysadmin/openobject-addons/branches/6.1/product/product.py", line 580, in name_get
    sellers = filter(lambda x: x.name.id == partner_id, product.seller_ids)
  File "/home/sysadmin/openobject-server/branches/6.1/openerp/osv/orm.py", line 478, in __getattr__
    raise AttributeError(e)
AttributeError: 31