I followed vb2ae's reply, thank you, to see what would happen. Just to make sure, I removed the reference and then re-added it. It is definitely pointing to the project. No change.
I try to keep the proprietary stuff from my questions and I think I create more problems that way. Let me try to clarify some things starting with the error.
Could not load type 'ProjName.FileName' from assembly 'ProjName, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
The file "FileName." is in the project and the reference points to the project. The test module Imports the project, but no the folder the FileName is in. The name of the folder has a space in it and it is not handled the same way that C# handles it. The program runs and there is no problem running the methods called in that particular file.
I get the same error regardless of the test I run. The only difference is the FileName.
I have updated all the Nuget packages. I have a perfectly clean build. I have unloaded and reloaded the Test project. I have cleaned and rebuilt the projects.
Thank you all.