Keep getting asked to sign in to Outlook "Microsoft Account"

I recently signed up to Office 365 and am using Outlook Web App.

In the past week when I click on my office 365 sign-in link I am redirected to a similar looking sign-in page, which has the blue Outlook Icon and is asking me to sign into my Microsoft Account which I don't have (the email and password I use for Office 365 do are not accepted).

1)  Why does my bookmark to Office 365 redirect me to a Microsoft Account which I don't have?

2)  Do I have to sign up to an MS Account to access Outlook Web App?

Thanks John