WordPress mobile error: “the target server failed to respond”

When joining a new mobile device to wordpress it looks like the first request is a GET request.

My Varnish config only included support for POST requests to xmlrpc.php

I updated my config to read:

// set backend, pipe, strip cookies from xmlrpc 
  if (req.request == "POST" && req.url ~ "xmlrpc.php") {remove req.http.cookie;set req.backend = mainserver;return(pipe);}
  if (req.request == "GET" && req.url ~ "xmlrpc.php") {remove req.http.cookie;set req.backend = mainserver;return(pipe);}

and it sorted it! Huraa