I Mattew, I apologize for the problem. It’s actually quite rare, but has been happening a bit more often over the past year or two, even though the related code has not changed since 2016.

It’s possible that there’s a temporary interruption in the internet, like my site going briefly offline (as it occasionally does). Simply trying again later on may solve the problem.

It’s also possible that something changed in the CORE plugin libraries I use. Hot Door created the CORE libraries for their CADtools plugin and also use it in their Control series of plugins. If you’re able to activate any of the Hot Door plugins, then there’s a good chance it can be fixed here, too. In one case, a customer from a large tech company could not activate a plugin in the office because of the communication error, so he took the computer home and successfully activated it from there. Yet other computers in the same office had no problem activating plugins. It’s an elusive problem, but I’ll continue to look for a solution. If you’re having this problem and do find a workaround, please let me know so I can share it with other users.