@aquila: the activation codes can only be used once. If the HDD was erased a new Operating system environment was installed from scratch, a new activation code will be required. If you didn’t, you may close the warning and ignore it, since the license has been already registered in the meantime.
@henrikfodgaard: it seems that the license has not been downloaded yet. The activation code for Wavelab LE 8 has not been used (see your MySteinberg account): Sign in
To download a license, open the eLicenser Control Center and hit the button “Enter activation code” and follow the instructions on screen to download the license. Further instructions on how to operate the eLicenser Control Center can be found here: http://www.steinberg.net/en/company/technologies/elicenser.html