This error is shown when attempting to use a currently activated license. For instance, Computer-1 has an activated license but you install RLP5 on Computer-2 and attempt license activation.
In this case, deactivate the license on Computer-1 and then activate the license on Computer-2.

For the license deactivation, please refer to:
How can I deactivate the license of RasterLinkPro5?

Notes
Even when the computer would not boot, you can deactivate the license on the Internet by “Deactivation (When the PC is broken)” function if you have another computer which is connected to the Internet. For details, please refer to FAQ: How can I deactivate the license when the computer has broken down?