之前安装了Cisco Anyconnect,没有正常删除anyconnect,而是直接拖到垃圾箱，发现不能重新安装anyconnect, 于是Google了一下，发现有解决方法。方法如下。

https://supportforums.cisco.com/t5/other-wireless-mobility-subjects/osx-removing-remains-from-unusual-anyconnect-uninstall/td-p/2401645

in Terminal.app:

sudo pkgutil –forget com.cisco.pkg.anyconnect.vpn

After that, you can reinstall the client.