This kind of problems used to happen with some customers. To check how you can solve it,please go through the link and do exactly the same as it is mentioned there :- http://btbusiness.custhelp.com/app/answers/detail/a_id/6032/session/L2F2LzEvdGltZS8...
Hi, Office 365 features can be accessed via a browser or an Outlook 2007 desktop client,Please check and compare here if you have applied all the correct settings :- http://btbusiness.custhelp.com/app/answers/detail/a_id/18555/~/getting-started-with-...