Referência: http: //developer.android.com/google/gcm/demo.html

Servidor 401 ao tentar enviar uma mensagem para o meu dispositivo Android.

HTTP Status 500 - HTTP Status Code: 401

type Exception report

message HTTP Status Code: 401

description The server encountered an internal error (HTTP Status Code: 401) that        prevented it from fulfilling this request.

exception

com.google.android.gcm.server.InvalidRequestException: HTTP Status Code: 401
com.google.android.gcm.server.Sender.sendNoRetry(Sender.java:177)
com.google.android.gcm.server.Sender.send(Sender.java:121)
com.google.android.gcm.demo.server.SendAllMessagesServlet.doPost(SendAllMessagesServ    let.java:83)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.29 logs.

Alguém poderia me dizer como resolver? Obrigado!