I think it is similar issue to this one: 404 for /lucee/res IIS BonCode
The problem is that my web server (IIS) is blocking the request to mapping-tag because it does not physically exist on the server. I also got this to work without the virtual directory in IIS by adding a blank file in the request location under the web root. This allows IIS to see the file and think it is there so it goes ahead and passes it through to Lucee.
I like this approach better just because it allows me to be more granular in the security settings that I can use for it. i.e. I can still block /lucee every where else.