It's the directory on my machine to which I have team foundation server mapped. At the end of the day forget the team foundation server portion. Originally I unzipped the source code to C:\Documents\NopUpgrade\nopCommerce_4.60.2_Source.
Opened the solution and ran the code without any issues.
I then took that same source code zip file and moved it to c:\productioncode\ and unzipped it. When I try to open the solution in the newly created directory all of the projects in the solution fail to load. Each with a .csproj error "The SDK 'Microsoft.NET.Sdk' specified could not be found.
Yet, if I go back to the solution in the original directory the solution loads and runs fine.
I can't figure out what nop is doing that would cause every project not to load when the source code is moved to a different directory.