Subproject in c# webapplication

Hi all,

I am new for creating the webpage. I need your guidelines.

I created main project and sub project as per the below procedure.

1. https://blogs.msdn.microsoft.com/webdev/2006/06/30/part-1-of-1-creating-sub-projects-in-iis-with-web-application-projects/

2. https://blogs.msdn.microsoft.com/webdev/2006/06/30/part-1-of-2-creating-sub-projects-in-iis-with-web-application-projects/

3. https://blogs.msdn.microsoft.com/webdev/2006/06/30/part-1-of-3-creating-sub-projects-in-iis-with-web-application-projects/

After that i create new page for sample i add url navigation it is working fine,  then i add the ajaxtoolkit updatepanel, scriptmanger. The webconfig is automatically add to the subproject and i am getting this error System.web.UI is missing and medata for subproject is not found. i am unable to open the page 

Error 1 The type or namespace name 'ScriptManager' does not exist in the namespace 'System.Web.UI' (are you missing an assembly reference?) C:\inetpub\wwwroot\Compass\SWHW\swhwhm.aspx.designer.cs 40 41 SWHW

Error 2 The type or namespace name 'UpdatePanel' does not exist in the namespace 'System.Web.UI' (are you missing an assembly reference?) C:\inetpub\wwwroot\Compass\SWHW\swhwhm.aspx.designer.cs 49 41 SWHW

Error 3 Metadata file 'C:\inetpub\wwwroot\Compass\bin\SWHW.dll' could not be found Compass

Kindly help me to what procedure to add the ajaxtoolkit 

Thank you.