I always have to click on that and say yes for Manifold installations.
Yes. That is as it should be. Microsoft wants to force vendors to participate in their monopoly system, so if a vendor does not participate in their monopoly system, Microsoft does their Fear, Uncertainty, and Doubt (FUD) thing. That is why that step is illustrated in the step by step Install and Activate topic.
I've had no luck doing an uninstall and reinstall and trying to activate the licence.
Do you mean you had no luck uninstalling? Or reinstalling? Or that you could do those OK but then could not activate? What happens when you launch the product after installing using the process in the Install and Activate topic? Do you get an Activation dialog?
after the reboot they all failed.
What does that mean? Did the applications launch an activation dialog? If so, that's not "failing," that is correct function.
Activation is really simple: you need an Internet connection and you can't have installed extra software that prevents Manifold from using Internet to contact the activation servers. It's hard to mess that up. You have to actively work at stopping activation from happening by installing software, like Trend Micro, that prevents Windows from functioning as it is supposed to function, or by having downstream hardware or software that blocks access to activation servers.
It is possible, of course, that some other utterly simple thing is going on. Classic examples are changing the serial number and expecting it to work, working with a computer system where the date is set to 1991 and expecting that to work and so on. That's why the Troubleshooting page has an explicit list of simple errors to check. Those are easy to eliminate.
If you want to solve the problem yourself, the fastest way to solve any activation problem is to follow the explicit and straightforward advice in the Troubleshooting page. Don't waste your time on anything else. For example, nowhere in the Troubleshooting page does it tell you to uninstall and to reinstall. It does tell you to install Microsoft prerequisites, but if you're using a Windows Installer installation that is done for you automatically.
In this case, the operative advice seems to be "Is any software installed that would prevent the Manifold product from contacting Manifold's activation servers? If so, turn it off or configure that software so it does not prevent Manifold from contacting activation servers. " I'd suggest doing that before you do anything else.
If you don't want to solve the problem yourself, contact Tech Support using the free activation support process. Note that you must provide full information as required for the process to be free.