Form_Closing() 事件中连续出现错误信息

如何解决Form_Closing() 事件中连续出现错误信息

我不知道这段代码有什么问题。每当我打开任何表单时都会弹出此消息框。

代码：

   Private Sub main_FormClosing(sender As System.Object,_
e As System.Windows.Forms.FormClosingEventArgs) _
Handles MyBase.FormClosing
        Dim dialog As DialogResult
        dialog = MessageBox.Show("Do you want to logout?",_
"logoUT?",MessageBoxButtons.YesNo)
        If dialog = DialogResult.No Then
            e.Cancel = True
        Else
            Application.ExitThread()
        End If      
    End Sub