MSSQL Error 'The underlying provider failed on Open'

Question

I was using an .mdf for connecting to a database and entityClient. Now I want to change the connection string so that there will be no

Answer 1

NONE of the answers worked for me

I think that some of us all make silly mistakes, there are 100 ways to fail ...

My issue was new project, I setup all the configuration in another project, but the caller was a Web Api project in which I had to copy the same connection string in the Web api project.

I think this is crazy considering I was not even newing up dbcontext or anything from the web api.

Otherwise the class library was trying to look for a Database named

TokenApi.Core.CalContext   

of which my project is named TokenApi.Core and the CalContext is the name of the connection string and the file name