How to prevent alert window from popping up on a Zen page

Probably not looking at the underlying code.

I would say its being raised by cspxmlhttp.js when it gets a non 200 status code.

If there was a sever side option then we would probably see some kind of conditional around either of these two functions...

function cspProcessResponse(req) {
  if(req.status != 200) {
    var errText='Unexpected status code, unable to process HyperEvent: ' + req.statusText + ' (' + req.status + ')';
    var err = new cspHyperEventError(req.status,errText);
    return cspHyperEventErrorHandler(err);
  }

...

}

function cspHyperEventErrorHandler(error)
{
  if (typeof cspRunServerMethodError == 'function') return cspRunServerMethodError(error.text,error);
  alert(error.text);
  return null;
}