Hi
I bought a upgrade for my sx3, cubase 5 upgrade bought second hand, when I try to register the upgrade at the Elicenser control center it tells me that it has been used before and only work one time, what am I to do to get a working activation code?
Make sure the seller followed this process…
Go through the steps yourself to make sure he/she did.
Regards 
If it has been used already, there is no way to get a “working activation code” for this update. The seller has to provide the USB key with the license on it, which you can then use without activating anything.