I'm not sure if you received some updates from Apple which have impacted the VPN Cert. If your CERT is showing as "invalid" you have to go into that CERT and set the IP Security field to "ALWAYS TRUST". You will have to do the same action for all of your work related CERT's (there may be serveral)
Input the following settings:
VPN Type: Cisco IPSec
Service Name: This can be anything, I left the default.
Edit the new interface details as follows:
Server Address: cisco.vpntraffic.com or other country vpn such as Denmark VPN
Account Name: Your vpn account
Password: Your vpn password