Comments by Michael Gledhill (Top 2 by date)

This is a very well known issue, and (in November 2016) has still not been fixed.

The solution is to delete/rename-out-of-the-way the "VSTOInstaller.exe.config" file in this directory:

C:\Program Files (x86)\Common Files\Microsoft shared\VSTO\10.0

Microsoft has responded to many complaints about this issue, but it hasn't been fixed yet (and our users don't have sufficient rights to delete this .config file.)