I recently experienced, for the second time, the case of the missing appointment actions ribbon in Microsoft Outlook. I was running 2010 when it disappeared, and was greatly disturbed by it. I found the article The Outlook ribbon disappears from Microsoft Outlook when you use the Microsoft Dynamics CRM Client for Microsoft Office Outlook on Microsoft Support. Sadly, I painstakingly fiddled with my registry as prescribed and found no relief.
It turns out that my problem was being caused by the iCloud plug-in. How did I determine this? Process of elimination. I went to File – Options – Add Ins, clicked on the GO button next to “COM Add-ins”, and then unchecked the iCloud add-in. Voila! All the meeting actions returned to view.