Cisco VPN Client Service Error

I am currently trying to fix a problem with one of our VPN users' computer.  We have a Cisco Pix 501 firewall which handles our VPN connections to work, each of the VPN client machines are running Cisco VPN Client 3.6.3.  There are no known problems with establishing a connection, I just don't seem to be able to get the client software working properly on a Windows XP Professional machine.  The program installs fine, however when it is run the error message I get is:

'The necessary VPN sub-system is not available.  You can not connect to the remote VPN server.'

I checked the Services from Administrative tools and the Cisco VPN Server (cvpnd.exe) was not started.  When I manually start the service the VPN client connects without a problem.  However, this is not practical and I can't work out why the service will not start when the system is booted.  I tried uninstalling/reinstalling/installing a more recent version, each leading to the same problem.  After checking event viewer the following error occurs during startup:

'Faulting application cvpnd.exe, version faulting module unknown, version fault address 0x0012e74c'

If anyone has fixed this problem before I would be grateful for your help.

Thanks in advance
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Hi dunelm_dave,
Do you have SP2 installed?
If you do then I recomend you install version 4.5 of the client.
dunelm_daveAuthor Commented:
Thanks for the quick response.

SP2 is installed on the machine, however I tried version 4.5 and the same error occured.  We have other windows XP professional machines running SP2 which can connect without problem using version 3.6.3, therefore I don't think it is a SP2 issue.
I have heard from others that the following procedure can help :-

1) Deinstall the VPN client
2) Reboot
3) Reinstall latest service pack
4) Reboot
5) Install VPN client.

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