We failed to reach a server. Reason: [Errno 111] Connection refused

A dedicated error message would be great. Unfortunately this "request and get response" is all handled within iOS - there is not much we can do about it, I guess.

catch the error and send response code of 500?

Catch which error?

I have not seen PlexConnect to stumble over the "//", yet it seems to be correlated with the error message you posted. 

Looking back to your original issues...

>> 20:33:06 WebServer: serving .xml: /webdefault/sample.php

Where does this request come from? Why us PlexConnect asked to server this /webdefault/sample.php? I am pretty sure, this request doesn't have it's source in iOS/aTV?

Why should answering with 500 help the aTV?