I think that you'll find that iZotope 9 Elements is linked to Samplitude and cannot be used with any other program. Did you try opening it with Samplitude Pro X5?
I have this invalid serial message from Isotope via Samplitude prox5 suite. But I instaled separately the applications, Not with the big package. So I instaled Sound forge 13 ( included in the prox 5 suite ) separately. I asumed it's a bit messy because the instalations were tricky to me in W10 and the whole proX5 suite package seemed to not work well. Do you think I have to uninstal everything and go back to the package ?