Cisco VPN client mysteriously stops working under Windows 8 -- symptoms: - connection appears successful - connection dialogue can still tell the difference between a right & wrong password, so authentication is working - network stats shows packets being sent and encrypted successfully, but 0 received / 0 decrypted - enabling the debug log shows corrupted IKE packets received with "invalid version (random version number)"; messages like: Sev=Warning/3 IKE/0xE300002C ISAKMP header invalid: Invalid version 10.14 found Solution: this happens when "Fast startup" is enabled (which does a partial hibernate rather than a real shutdown / startup); if the VPN driver is connected at shutdown, it gets confused next startup. Disable fast startup: Power options > "change what closing the lid does" > enable options not currently available (link at the top) > "enable fast startup" (checkbox at the bottom). Then do a full shutdown and cold start.