Hi there!
There are no restrictions on subfolders - only on sub-applications. The problem would be if your admin piece is a separate application that requires being in a subfolder. For example, you should have no problem if you have just one application, physically located in the c:\AppFolder and mapped to a Cassini applications http://host:port/. Then your admin piece should be accessible as http://host:port/admin/, provided its files are located in c:\AppFolder\admin folder.
If you provide your application's physical and http locations, along with the URL to the admin piece that fails, we should be able to troubleshoot it for you.
Best regards,
UltiDev Team.
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