iZotope has had a number of installation/activation problems in the last year or so. Remember, there are two ways to install an iZotope product -- directly, with the specific product installer [which is what I always use], or via their Product Portal software [if you used the Portal you might want to try the regular installer]. This page from iZotope support discusses troubleshooting some common authorization issues and includes links to other support pages on Authorization problems:
That said, you'd probably need to provide them with more information: platform, OS, OS version, Nectar version, etc.. You said "it died after iZotope's update in recent weeks"; was it installed|working properly before you updated Nectar? When you say "cannot activate" exactly what happens?