It looks like a number of publishers are changing the way that Athens users login to their websites. When you attempt to login to a publisher or database website, you are advised to follow the Athens links until you are presented with an option to enter your NHS Athens username and password. This advice still holds. However at some point you may be presented with 2 Athens options; one of which is OpenAthens. If this occurs the OpenAthens option is the link you should click to then go on and enter your Athens username and password.
Eduserv / Athens offer various versions of their authentication system and the NHS uses the OpenAthens MD version.