Problem
A corrupt install of the VPN client won't uninstall. Users cannot re-install, as message says to uninstall product first.
There is no Cisco VPN client listed in Windows add / remove programs.
Solution
Go to "Regedit" and search for "Deterministic Networks" and delete it.
HKEY_LOCAL_MACHINE \SOFTWARE\Deterministic Networks
Search with the following keywords in the registry, under "Uninstall" or "Components" folders and delete any related entries.
Vpnapi
Vpngui
Cisco
CVPND
CVPNDRA
Ipsecdialer
Source: https://supportforums.cisco.com/message/3728011#3728011