I have a project with Win32 and x64 configurations. Test launching (all varieties) was failing with a message about unable to find the specified path
It turned out I had changed the output path for the x64 build, but not the Win32 build as this project won't ever be used 32-bit. The AddIn appears to be always picking up the Win32 configuration regardless of the actively selected platform.
Poking around with the code the culprit seems to be Connect.cs:345
l_vcConfig = l_vcProj.Configurations.Item(applicationObject.ActiveDocument.ProjectItem.ContainingProject.ConfigurationManager.ActiveConfiguration.ConfigurationName);
This line was finding the Win32 configuration rather than the x64 one. I will add a patch that fixes the problem. I don't know the available APIs for AddIns at all so there may be a better solution that iterating through all the configurations as I have done.