The Activate Online... option on PlayIt Software products use an embedded web browser to enable activation. The activation page requires cookies to be enabled to allow you to log in. If you try to log in with the correct email address and password but are still redirected back to the log in page this means that cookies are not enabled on the embedded browser.
To enable cookies go to Start and type Internet Options. Choose the Privacy tab, decrease the slider to at most Medium High and click OK.
Now try to log in via the Activate Online button.