我正在尝试从我的家用电脑上使用“Microsoft Office Communicator 2007 R2”。我已连接到公司网络的 VPN，安装了 Microsoft Office Communicator 2007 R2，现在尝试连接它，但有时只能连接。大多数情况下，它会给出错误
"Cannot sign in to Communicator. You may have entered your sign-in address, user name, or password incorrectly, or the authetication service may be incompatible with this version of the program. If your sign-in information is correct and the problem persistes, please contact your system administrator."
有人能告诉我这是什么原因吗？我该如何在第一次尝试中通过 VPN 连接到我的办公室通讯器？
谢谢！