This document describes common mistake when end-user recieve error "HTTP 501 not implemented".
By default, the Cisco WSA runs the web GUI on TCP port 8080. The GUI web server running on port 8080 is attempting to respond to the client traffic instead of the proxy.
Typically, all traffic that comes in to the WSA GUI on port 8080 will be redirected to the HTTPS web GUI. This causes the client to send an HTTP CONNECT request to the GUI web server, which does not allow this type of connection.
The browser must be set to use one of the proxy ports configured on the WSA. To verify or change which ports are enabled for Web Proxy traffic, go to: