Configuration Manager is missing in C# Visual Studio

Explanation:

The error occur when you keep your database connection string in Config file, and when you are retrieving your connection from Config file, you are using

string str = System.Configuration.ConfigurationManager.AppSettings["myconnection"];

But it shows the error

Solution:

Just go to Solution Explorer in your visual studio and right click on Reference and select add reference, in the new window select System.Configuration and click Ok.

Your Problem Solved!