VS 2017 Metadata file '.dll could not be found
The problem was that I had some other normal error messages in my project, and apparently after I fixed those and when I cleaned and built my project AGAIN, then all .dlls succeeded.
Make sure you don't have any other error messages in your project and if you do, fix those first!
Steps in Fixing this Error: MetaData File .dll could not be found.
Clean All Projects.
Unload All Projects.
Reload All Projects.
ReBuild Solution.
Then problem solved.
In my case, there was an error, but it was not properly parsed out by VS and shown in the "Error List" window. To find it, you much view the ol "Output" from build window and parse through the messages starting from top down and resolve the actual error. M$, please fix! This is a huge waste of time of the worlds collective developers.