Synopsis
ASP.NET applications inherit any .config files in parent applications.
When this occurs, you may get errors such as: "Could not load type 'AspDotNetStorefront.RegisterRoutes' from assembly 'App_Code'"
So if you want to run a standalone application in a virtual subfolder, you must stop ASP.NET from inheriting the web.config file.
Procedure
The following code must be posted before the <system.webServer> tag in the {root} web.config file of the parent site:
<location path="." inheritInChildApplications="false">
<system.webServer>
and close the location tag after the system.webServer closing tag:
</system.webServer>
</location>
And also wrap the <system.web> tag immediately following the </appSettings> tag.