You tried to register to a website created with the ‘META Innovation Platform’, using an email address which you've already used in another website created with the ‘META Innovation Platform’.
All of these websites are built on top of the same database, so simply use your account from the first site on all of them. If you forgot the password, simply use the ‘forgot password’ function on any of them.
This, by the way, brings you a number of advantages:
If you need help with an existing site, please use the help services provided by that site.
If you would like to know more about the META Innovation Platform, check out the Home Page and FAQs, or simply Get in Touch.