MessageBox appears twice [closed]

I have the following code which is fired by Handles Button1.Click .

Dim X, Cf As Double
    Dim A, B, C, D, J As String
    A = TextBox2.Text
    B = TextBox3.Text
    C = TextBox4.Text
    D = TextBox9.Text
    J = ComboBox2.Text
    If J = "K" Then
        If W5() = "K" Then
            If A = "" Then : C1() : Else : X = TextBox2.Text : End If
        ElseIf W6() = "K" Then
            If B = "" Then : C1() : Else : X = TextBox3.Text : End If
        ElseIf W7() = "K" Then
            If C = "" Then : C1() : Else : X = TextBox4.Text : End If
        ElseIf W8() = "K" Then
            If D = "" Then : C1() : Else : X = TextBox5.Text : End If
        End If
        If X <> Nothing Then
            Cf = ((X * 78) / 94) / 100
        End If
    End If

Being C1() a warning message when the W (5 a 8) chosen is empty.
My problem is that when W is empty the MessageBox of C1() Appears twice, if W is not empty everything happens as scheduled. This is the code for my MessageBox:

Public Function C1()
    MessageBox.Show("Informe o valor!", "Atenção", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
End Function

Could anyone help me here? C # answers are also accepted.

I apologize to everyone who took some time off to help me, the code was being fired twice, now it's back to normal. Thank you all for the help.