Problem solved
This was driving me crazy.
Inside ~/App_Start/RouteConfig.cs change:
settings.AutoRedirectMode = RedirectMode.Permanent;
To:
settings.AutoRedirectMode = RedirectMode.Off;
(Or just comment the line)
Also if friendly URLs are enabled you need to change
url: "ConsultaPedidos.aspx/GetClients",
To:
url: '<%= ResolveUrl("ConsultaPedidos.aspx/GetClients") %>',
Hope this help somebody else