Is there any message with the die?

Short of details, I've just another wild guess: If your browser receives a second click event while the first one isn't processed completely - maybe the client aborts the first request in a way the server doesn't expect? Inspect the error handling in case your server can't send the response (because the client closed the connection) or received an incomplete request (because the "click" caused either a lengthy POST request or some local JavaScript action which was aborted by the browser).