If you have a multi-PC license, then using a 3 PC license is what you should have. You shouldn't have any issues running your vpn's on more than one machine.
However, if you have a license for only 1 PC, you'll need to remove your copy of your license from the other PC you are not using and apply it to the one you wish to use to make it work there. You'll also need to remove the Securline VPN feature from the PC you won't be using the license for and then enable that feature on the PC you are using.
If you don't do the above, and have a single PC VPN license, you'll get the error you are seeing. "Your SecureLine VPN license has been refused.", when you try to use the same 1 PC license on two machines at the same time.