How to fix: SharePoint Online won’t open documents or attachments in client applications (eg in Word or Excel on the desktop)

This is a frustrating problem

There are two steps

Step 1. Enable the “Open Documents in Client Applications by Default ” service – see steps here: http://support.microsoft.com/kb/2859986

Step 2. Check the Library Settings –> Advanced Settings–> Opening documents in browser is set to “Use the server default (Open in the client application)”