I got this to work with the following code but would like some further thoughts and best practice ideas for how this could be better accomplished.

    ' Validate the CompanyLogoShape
    Public Function ValidateCompanyLogoShape(ByVal companyLogoShape As String) As String
        Dim message As String = Nothing

        Dim testResult As Boolean = companyLogoShape.Equals("Square")

        If companyLogoShape.Equals("Square") _
            OrElse companyLogoShape.Equals("RectangleLandscape") _
            OrElse companyLogoShape.Equals("RectanglePortrait") Then
        Else
            message = "Logo Shape must be Square, " _
            + "RectangleLandscape, or RectanglePortrait"
            Me.AddErrorProviderBrokenRule("CompanyLogoShape", message)
        End If
        Return message
    End Function