I know that I had the same problem a while ago. In my case, brothers and sisters participated in two applications, and not one of them. The problem was that web.config in the root directory (above two sites) conflicts with web.config on separate sites. I solved this by simply deleting the root web.config (since nothing works in the root.
So my advice (I know for sure that this is not a solution) is to check for conflicts in your web.configs.
source share