尝试杀死adb服务器并通过命令提示符重新启动

Try Killing the adb server and restarting it thru command prompt

go到你的android skd目录，你曾经保存它
并遍历到adb.exe你会发现在平台工具..

go to your android skd directory where ever you have kept it and traverse to adb.exe which you will find inside platform-tools..

可能是这样帮你。同样发生在我身上多次。当时我刚刚重新启动服务器

May be this will help you. same happened with me many times. I just restart the server at that time