If you get this error upon trying to install Cisco Anyconnect:
Key Not Valid for Use in Specified State
Danish translation:
Nøglen er ikke gyldig for anvendelse i den angivne tilstand.
Do the following:
Move the folder RSA from
C:\Users\AppData\Roaming\Microsoft\Crypto\RSA to say C:\RSA (just in case there should be a need to restore it) then try installing again.
This folder appears to act as a cache and should be rebuilt automatically as required.