Microsoft Office Sign-In does not work. Cannot save the document :(
Many people I know get frustrated when the office does not allow you to sign in the document after you have done some changes. This is really, really annoying.
It is frustrating and the ultimate killer of the creativity.
So, here is the solution for all of you who are advanced Windows users.
Go to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, delete the identity with the issue.