So yesterday I upgraded to 10.4.10 only to discover my Cisco VPN is not working anymore. It gives an Error 51... That was real bad since I have a client that I support using VPN.

I tried everything to revert to 10.4.9 but it is not that easy to roll back a service pack. Eventually I stumbled across an article on Parallel's forum indicating that my problem might be related to the fact that yesterday I also upgraded from 4124 to 4128...

I did the following to fix it:

1. Disabled the fw0 interface (this only fixed the Error 51 - it loaded VPN client but I could still not make a connection)
2. Uninstalled Cisco VPN
3. Uninstalled Parallel
4. Installed Cisco VPN
5. Rebooted
6. Started Cisco VPN and connected successfully to remote VPN site
7. *Whilst being connected to my remote client, I reinstalled Parallels.
8. Rebooted
9. Everything is working!

So a word of caution - never install two updates simultaneously.