Apple and Microsoft - a mixture made somewhere. Do support for a small local non-profit where they use Office365 and a number of staff have Macs. The executive director is currently in Europe and Word was nagging that she wasn't signed in greatly limiting the functionality. Advice from Technet - go into Keychain and nuke the Microsoft Office entries. Bloody things won't die Look up how to fix the problem. First suggestion is keychain first aid. Turns out Apple killed a few major versions ago. Next suggestion - reset on keychain and re-import. yeah not doing that while she's a long long way away. Further search reveals something almost unheard of. A piece of useful information in Microsoft's tech support forums linking to app some-one had written that fixed the login issue. Anyway all is good now.