I have one knowingly good site. It works as expected. I copied all the files from that one directory to a new directory. I created a new website with the correct host header and pointed it to the new directory. When you browse to the new site you get a 404 error.
I have checked the file permissions. I have even made the two sites share the same app pool.
Any suggestions would be helpful.
If you look in /App_Data/Logs you can see the error message. As it turned out for me, it was because I was trying to run the same “tenant” twice on the same server.