Hi there, I would first recommend that you move away from the legacy IPSec VPN client and move to an AnyConnect based solution. The IPSec client has been End-of-Life / End-of-Sale for a while now and it has not been supported since Windows 7. With that being said, I have actually seen the VPN client installation break windows and require windows re-installation.
However, if you must stay with that client, I would suggest trying the suggestion in this link:
http://techbastards.com/internal-error-2502-and-2503-installing-or-uninstalling-programs-in-windows-8/
I hope this helps!
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