Have reinstalled Redunoise several times and made sure that no other instance was anywhere on the machine.
I go to the correct link to register the plugin and it seems to take.
Reaper is happy.
The instance in WaveLab keeps saying it is unregistered.
What could be causing this that I've hopefully just overlooked?
I have no idea, but I initially tried running WaveLab as admin, and it didn't work that way.
A few days later I go to the program links and changed them to run as admin there, and it now works.
Okay. As the Windows world gets ever more convoluted....