FileSystem Web site to IIS Express.
- Open VS2015 (Right click and select Run as administrator).
 
- Click File > New > Web Site...
 
- In the New Web Site dialog, click Browse... button.
 
- Select Local IIS in the left pane. And select IIS Express Sites in the right pane.
 
- There are 4 buttons in right side on top. Click Create New Site button.
 
- Give name and click Open.This will select HTTP in Web location.
 
- Click OK.
 
- Then close the solution.
 
- Open applicationhost.config from
Users\\Documents\IISExpress\config folder. You can open in the notepad.
 
- Find your web site in sites section. And change the physical path
 inside (virtualDirectory path="/" physicalPath="C:\WebApp\WebSite1"). Write the path of your existing Web Project.
 
- Save and close applicationhost.config file.
 
- Run VS2015 (Run as administrator).
 
- Click File > Open > Web Site...
 
- In the Open Web Site dialog, select Local IIS from left pane.
 
- Select your site under IIS Express Sites and click Open.
 
- Click Web Site menu and New Virtual Directory...
 
- Give Alias Name and Folder path and click OK.
 
Now you can create it without error.