Redirect to custom page with FormsAuthentication using C# in ASP.Net

http://localhost:3834/Default.aspx?ReturnUrl=%2fState%2fGabbPage.aspx

it refused to redirect after login i dont know if its from my web.config file

<compilation debug="true" targetFramework="4.5">
      <assemblies>
        <add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
        <add assembly="System.Web.Extensions.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
        <add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
      </assemblies>
    </compilation>
    <authorization>
      <deny users="?" />
    </authorization>
    <authentication mode="Forms">
      <forms defaultUrl="Categories.aspx" loginUrl="Default.aspx" slidingExpiration="true" />
    </authentication>
  <pages>
      <controls>
        <add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />
      </controls>
    </pages></system.web>
  <appSettings>
    <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
  </appSettings>
</configuration>