Could you check if you are using the Fast User Switch feature on the machine you are experiencing the problem with? If it is on, please turn the feature off, and try again.
make sure that the group on the VPN3K has "Keep SSL Client" enabled
run SVC as an Administrator to have all the necessary components installed
As a Power User :
put the VPN3K in the Trusted Zone in order to have ActiveX enabled
As a "Simple" User :
put the VPN3K in the Trusted Zone in order to have Java enabled
make sure that a proper JVM (Sun, > 1.4.x) is installed and usable
The reason why you have to use the JVM for the "Simple" User is that, even when ActiveX is marked as Enabled, the user does not really have the permission to use it, and therefore SVC has to fall back on the JVM.