This information applies to version(s): 2018, 2, 3, 4, 5, 6
First of all, please make sure that an internet connection is available.
Is an anti-virus/firewall/proxy or other security tool running which might be blocking the activation? If so, please try temporarily disabling it, and see if the activation succeeds.
If you are on Windows, right-click the program icon and choose "start as administrator", and see if that allows you to activate.
If this does not work, please contact customer support and provide a screenshot (jpeg) of the error you see when trying to activate, so that our customer support can assist you.
To get help from DxO Support Team directly from this page, please click on this link.