Cannot compile project

I have an existing asp.net core application. Recently, I've added a new class library. It compiles fine. When I add a reference to my original asp.net core web api, I get "error CD0006, Metadata file ***.dll could not be found." 

I've tried removing and adding the class library project.

Re-opening VS.

Deleting project.json.lock... 

Nothing worked. It's looking for the class library .dll in the wrong path. How can I fix that?

Thanks

--tolga