This is horrible. 
Yesterday I noticed that my version of Cubase Pro 9.0.30 had blacklisted Reaktor 6. I tried to reactivate it and cubase crashed instantly. So Cubase 9.0.30 will currently open but Reaktor is blacklisted and unable to be reactivated. I have Cubase Elements 9.0.20 on my computer and opened that. Reaktor was also blacklisted but this time if I reactivated it Cubase wouldn’t crash. This morning I went to open Elements and Cubase crashes on loading. I can’t even get the program open. I have an old version of 8.5 still on the computer and I tried that…and crash on load as well! Good times!
Try to re-install Reaktor 6.
Yes I have. It did not help. I just removed the Reaktor 6 VSTs from my VST folder and the programs open now. Someone else posted that 10.11 works on their computer. I’m running 10.10 and I definitely have no plans to update. I don’t know if it’s an OS thing or what. I guess I am not hoping to find an older version of the VST in my backups.
UPDATE: Native Instruments got back to me with a link to Reaktor 6.1.1. I installed it and Cubase is back up and running! So watch out folks for that Reaktor 6.2 update!