Office 365 (Known Issues) - Sign Out Error in Safari
When logging out of Office 365 in Safari, a "Sign out error. Browser blocks cache cookies... " notification displays.
Resolution Status: Unresolved
Workaround
Disable blocking of cookies in Safari:
1. Go to File in the upper left-hand corner and select Preferences.
2. Click the Privacy tab.
3. Select Never in the "Block Cookies" section.