The underlying provider failed on Open.

one of my friends send me this example to learn about entity framework

but it always show me the following error: "The underlying provider failed on Open." in this code:

        Public Function GetAllDepartments() As IEnumerable(Of Department) Implements IDepartmentRepository.GetAllDepartments
            Return Me.context.Departments.ToList()
        End Function

You can find the program in the following link: http://www.grupossc.com/VB.zip