We have an application that has been in production for several years. Several weeks ago there were a group of Office updates, one of which caused errors in some office programs, like if you looked at your Outlook calendar Outlook crashed. Good times...

After that was sorted out the application, on one computer, began experiencing these sorts of errors;

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)

The code varied.

So I compared the updates with that of a PC not having the issue.

I ran the office repair.

I ran DISM and SFC.

I created a cross .dll trace facility to see exactly where the error was occurring.

Nothing helped.

Then I remembered I had an issue with excel interop that was cause by an add-in. When I compared add-ins, the good PC's had Acrobat PDFMaker, the bad did not. I was convinced that was not the issue since word interop was failing mostly on simple saves.

But out of frustration I installed Adobe Acrobat. Guess what.

No more issues. W_T_F over!