You receive this error when compiling your application with Visual Studio .NET in Iron Speed Designer:
Unable to compile application. A virtual directory must exist when compiling with Visual Studio. Please create a virtual directory by hand for ‘http://localhost/XXX’ that points to the physical directory “C:\YYY”, then try building again.
This error can sometimes occur when you are not running ‘localhost’ as the web server, even though a virtual directory already exists for your application.
Place a dummy file called 'get_aspx_ver.aspx' in your application’s project folder. The file can be empty. (You can Google 'get_aspx_ver.aspx' to get an explanation of why this works).
Part VII: Troubleshooting Applications
Application Generation and Compilation Error Messages