mvcmembership & structure map

I'm trying to include mvcmembership in my project but i cant get it to work with structure map.
where what i'm doing in the Bootstrapper:
Scan(assemblyScanner =>
            {
                assemblyScanner.TheCallingAssembly();
                assemblyScanner.Assembly("MvcMembership");
                assemblyScanner.WithDefaultConventions();
            });


Error:
StructureMap Exception Code:  202
No Default Instance defined for PluginFamily MvcMembership.IUserService, MvcMembership, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null


Anyo ...