Android gcm服务器获取HTTP状态500-尝试6次后无法发送消息

我已经成功地在gcm_演示页面上注册了我的设备，消息如下“1台设备已注册！”

但当我单击页面上的“发送消息”时，结果是：

HTTP Status 500 - Could not send message after 6 attempts
type Exception report
message Could not send message after 6 attempts
description The server encountered an internal error that prevented it from fulfilling this request.

例外情况

java.io.IOException: Could not send message after 6 attempts
    com.google.android.gcm.server.Sender.send(Sender.java:136)
    com.google.android.gcm.demo.server.SendAllMessagesServlet.doPost(SendAllMessagesServlet.java:83)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

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请通过添加代码和修复语法来改进您的问题。提供重现错误的步骤。即您的配置和代码片段。