One version of the text of the 502 error reported by an Apache server says "The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request. This may be a temporary or permanent condition, please try again at a later time." This is appropriate where the proxy server encounters a problem accessing the remote server where the remote server either 1) reports some sort of error or 2) is unreachable either temporarily or for an extended amount of time. The case of (2) is supposed to be a "503 - Service Unavailable" or "504 - Gateway Timeout" but I guess this is open to interpretation by the implementor of the proxy. Needless to say there are any number of things that can cause this, none of which necessarily place blame specifically on the proxy server, the internet connection between the proxy server and the remote server, and the remote server itself.
AOLserver only reports 502, 503, and 504 errors when specifically instructed to do so. I've seen proxy code do this and some really weird server-to-server protocol handler stuff as well. Kris
