Original title: Office 365 error message?

Error Message: You're currently signed in with an Office 365 email account, which can't be used with Outlook.com. Please click here to sign out of your Office 365 account, then use another Microsoft account to sign in to Outlook.com (for example, your hotmail.com, live.com, or msn.com account).

I have never had this message and I haven't changed how I sign in to my account. I'm not sure what has changed.

Could someone tell me what this means and what I need to do?

Thanks!