'How to close all open forms in a multiform app
'put this in the form_closing event of your main form

 Private Sub frmMain_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing


        '---make sure to close all forms
        For Each myForm As Form In My.Application.OpenForms
            If myForm IsNot Me Then
                myForm.Close()
            End If
        Next

    End Sub