I try to activate Skalp for SketchUp and my computer complains that all my activations have been used
You are allowed to activate one Skalp license on two computers. If you want to transfer to a third computer, you need to deactivate one of your Skalp installations. Your computer needs to be connected to the internet to use this procedure. From the top menu choose: Extensions > Skalp > Tools > Deactivate on this computer. After doing so you can reactivate using your original license activation code. There is no limitation on how many times you can transfer your license.
If you get this message and Skalp is not already installed on two computers or for some reason you can’t deactivate it anymore. Please contact firstname.lastname@example.org.