1. 平时连接TFS服务器很正常，有一天突然连不上了，并且显示以下信息：
---------------------------
Microsoft Visual Studio
---------------------------
Team Foundation Server
TF31001: Team Foundation cannot retrieve the list of team projects from Team Foundation Server server-***. The Team Foundation Server returned the following error: The request failed with HTTP status 503: Service Unavailable..
---------------------------
OK Help
---------------------------
2. 先Google，尝试了很多方法，问题都没有解决
3. 再仔细查看错误窗口信息，发现 The Team Foundation Server returned the following error: The request failed with HTTP status 503: Service Unavailable，所以猜测web service 有问题，接着检查IIS Application Pool，发现"Microsoft Team Foundation Server Application Pool"的状态为"Stopped"
3.1 启动 Microsoft Team Foundation Server Application Pool
3.2 使用 Team Explorer 连接TFS服务器，仍然失败
3.3 再次检查 Microsoft Team Foundation Server Application Pool, 状态又变为 Stopped了
4. 查看系统日志：
The identity of application pool Microsoft Team Foundation Server Application Pool is invalid. The user name or password that is specified for the identity may be incorrect, or the user may not have batch logon rights. If the identity is not corrected, the application pool will be disabled when the application pool receives its first request. If batch logon rights are causing the problem, the identity in the IIS configuration store must be changed after rights have been granted before Windows Process Activation Service (WAS) can retry the logon. If the identity remains invalid after the first request for the application pool is processed, the application pool will be disabled. The data field contains the error number.
4.1 想到上周域帐号密码变了，可能是域帐号密码变化导致的
4.2 查看 Microsoft Team Foundation Server Application Pool 的Identity，发现使用的帐号果然是变化密码的那个
4.3 将密码更新
5. 使用Team Explorer重新连接，一切Okay!