Cisco VPN Client Blue Screen upon Connection

I’ve suffered with Blue Screen on my Windows XP when trying to connect with Cisco VPN Client. The crash happened right after the connection. Turned out there was two firewalls fighting - my Comodo Firewall and Cisco’s own firewall. Luckily, solution was found:

Cisco VPN client installs ZoneAlam Firewall and thus it conflicts with Comodo Firewall causing BSODs.

Resolution:
1 - Search your computer for vsdatant.sys and vsruledb.dll files.
2- Delete these files
3- Reboot your PC

source: forums.comodo.com