Exactly which version and variant of MEP are you trying to install?
Have you seen this thread, where another user has encountered the same problem? It seems, from that thread, that the problem eventually resolved itself.
I am in process of restarting my computer after updates. I have windows 10 and I just purchased MEP 2021 Plus. I got that notification for 2 or 3 out of the ten additional installations. Did not complete the installation. I will try turning off ransomware during installation.