Word Horizontal Ruler tab stop toggle button

[Jon_A_G]

My Word 365 Horizontal Ruler tab stop toggle button is greyed out. Does anyone know how to fix this issue? TYIA

[#2]

@Jon_A_G Do you mean the button that allows you to select the type of tab stop?

Has some form of protection been applied to the document?

[#3]

@Doug_Robbins_Word_MVP 

Yes, that’s the button. No protection has been applied. It suddenly appears this way for every document, including brand new dox. 

[#4]

Try performing an On-Line repair of the Office installation as detailed in the Knowledge Base article at:
https://support.office.com/en-us/article/Repair-an-Office-application-7821d4b6-7c1d-4205-aa0e-a6b40c...

[#5]

@JanTrusso Which would be?