Cannot find namespace 'System.Data.SqlServerCe'

Question

I did include the System.Data.SqlServerCe dll, put using System.Data.SqlServerCe; in my code, but when I open the .NET page I get:

Answer 1

This is pretty late for answer. But I also faced the same kind of problem.
I am using Visual Studio 2012 and Visual Studio 2017 and I found the System.Data.SqlServerCe here.
The same directory for both Versions.

I edited @JesiMov Answer.

Right click the References folder and select Add Reference... option.
Go to the Assemblies | Extensions option on the left pane, then scroll to System.Data.SqlServerCe in the right pane.