VC call webservice Authentication Problem

I am trying to follow the tutotia l(Tutorial 1: Modeling a Simple Application ) of VC in CE72 at http://help.sap.com/saphelp_nwce72/helpdata/en/44/d958673ef05f4de10000000a11466f/frameset.htm. When run the model, error 401 occurs when call the webservice. I tested webservice successfully by right click the data service. however, it need enter UID/Pwd(In NWA-> SOA Manager, Single service admin, it doesn't allow no authention). I think the problem is bwteen user mapping beween VC(EP) and webservice. Any one know how to define such a user mapping in EP?

I created a system object in EP, but cannot find it in user management. Thanks!