System.Configuration.ConfigurationManager not found

If you added the reference in your code already:


using System.Configuration;

but still the System.Configuration.ConfigurationManager.ConnectionStrings is not found in your code, looks like you need to manually add a reference to the System.Configuration.dll file.

To add the System.Configuration follow the next simple steps:

1. Righ click on the references folder
2. Select Add a reference
3. Select Assemblies >> Framework
4. Search for the System.Configuration and select it
5. Click the Add button