I recently had a situation recently where I had a stale VPN session that I needed to kill in ISA 2006. I opened the ISA console and navigated to Monitoring >> Sessions tab.

After editing the filter, I could see all active VPN sessions, I right clicked the session that I no longer wanted active and selected ‘Disconnect VPN Tunnel’.

I was presented with the following error:

Solution:

You can kill an active VPN session by opening the RRAS mmc snap-in to manage the active VPN sessions.

You can then Right Click on the user whose session needs to be killed and Disconnect