Cisco VPN Mac Problem Workaround
I've been getting this error recently using the Cisco VPN Client on the Mac:
Error 51: IPC socket allocation failed with error 4h. This is most likely due to the Cisco Systems, Inc. VPN Service not being started. Please start this service and try again.
Turns out that for me, turning Internet Sharing off makes this error go away.
Bring up System Preferences, type 'Internet Sharing' in the search box and hit Enter, and then hit Stop on the Sharing tab that shows up.