Alguns dias atrás, eu tive exatamente esse problema e a única maneira de corrigir esse problema foi desinstalar e reinstalar o Office.
Para desinstalar o Office, usar FixIt :
Click Fix it.
At the bottom of your screen, click Open.
NOTE: If the file doesn’t open, click Save > Open Folder, then double-click the file (it should start with "O15CTRRemove") to run the Fix it tool.