Two machines. Both with .NET 3.5 and the VS 2008 VC++ SP1 redistributables
A single exe which uses two signed DLLs, one in C++/CLI and one in C#
The exe load
The SN.EXE is Missing in Newer versions of Visual Studio. In Visual studio 2012, we must use "Developer command prompt for Visual studio 2012". Then Run the command "sn".
Syntax: sn -Vr *,2d58152b8e842be2
where "2d58152b8e842be2" is the public key token shown in the Error message. Somehow this alone did not solve my problem.