Installing VSTO 4.0 Causes VSTO 3.0 Addin to quit working

Question

I just installed Visual Studio 2010 yesterday. As part of that I installed VSTO 4.0. Now when I run any Office application, my VSTO 3.0 addins fail to load. The error in

Answer 1

It turns out that VSTO 4 doesn't trust add-ins on network locations by default. However, by adding the following registry key

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\vsto runtime Setup\v4]
"EnableVSTOLocalUNC"=dword:00000001

and re-enabling my add-in, it appeared to work as expected again.

Another option for some is just to install the add-in on the user's local machine instead of on a network location