I used the latest install version and copied all the install files to c:\inetpub\wwwroot\yaf\. yaf is an application under my local IIS.
Everything ran well in the browser after the successful install and I was able to go to various pages without any issues.

However, problems showed up when I opened the above website in VS 2015 and tried building the application. I got the following build error that seems impossible to correct.

C:\inetpub\wwwroot\yaf\pages\reportedposts.ascx(2): Build (web): The virtual path '/controls/ReportedPosts.ascx' maps to another application, which is not allowed.
C:\inetpub\wwwroot\yaf\pages\reportedposts.ascx(85): Build (web): Unknown server tag 'YAF:ReportedPosts'.

Question
Why is this error showing up in VS 2015 even when all the install files have been correctly copied to the yaf website?

I think this is a bug with code front for pages/reportedposts.ascx.

When I changed ../../controls/ReportedPosts.ascx to ~/controls/ReportedPosts.ascx then no build errors were reported in VS 2015.

So, I ended up using the following line in pages/reported.ascx.
<%@ Register TagPrefix="YAF" TagName="ReportedPosts" Src="~/controls/ReportedPosts.ascx" %>

The original line in same file was, which I think is not correct since it throws a build error.
<%@ Register TagPrefix="YAF" TagName="ReportedPosts" Src="../../controls/ReportedPosts.ascx" %>