Searching the forum, I have found several post related to this but not exactly describing the issue I am having precisely.
If you are trying to run Cisco VPN client 5.0.xx together with ZAISS 10.0.x, and if the server request you to have the Cisco stateful firewall of the VPN client enabled then forget it...
Cisco firewall need the vsdatant.sys (located in C:\windows\system32\ directory) to run, Cisco VPN client uses the version 7.0.462.0 of this file, which is replaced by version 10.0.xxx.x when installing ZAISS version 10 (10.0.250.0 if you use the latest version).
As this file is used (and therefore locked by ZAISS), installing Cisco VPN client after ZAISS will not solve the problem.
The only way I got the VPN client to work was to completely uninstall ZAISS.
I have contacted support, they are working on the issue for the next release apparently... but no date obviously... they advised me to go back to version 9 of ZAISS as it was working then... not great choice, but if it's the only one then I'll have to.
Hope this is somehow useful to other users.