Recently I ran across an issue getting my outlook 2013 CRM plug-in connecting to our Office 365 CRM instance. I ran through the typical solutions:
I changed my password and removed the @ character. Once I changed my password to a different special character, everything worked well. This character did work for me the past and I was always able to authenticate, so I’ll be doing some testing to see if it was the simple act of changing the password on-prem (dir-sync’s to O365) that did the trick.