Not Acceptable
An appropriate representation of the requested resource /aa/bb/cc.php could not be found on this server.
Additionally, a 404 error was encountered while trying to use an ErrorDocument to handle the request.
Receiving this error, what does it refer?
I understand that the page is denying access to resources, but what might be the reasons for this?
This is a content type problem. Probably the request or response is using a mime-type that the server or the client can not handle. It can also be an invalid charset or encoding . It may still be an invalid language or resource size. Probably one of the two sides is misconfigured. Most likely you are getting this on some specific client that is not ordering correctly.
As there are no details, you can only respond generically.
