[alma2]

اذا كان قصدك تريد شكل Indeterminate بدل شكل Checked ولكن تبقى المسألة بحالتين فقط

كود :

Public Class Form1

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Label1Check()
    End Sub

    Private Sub CheckBox1_CheckedChanged_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        If CheckBox1.Checked Then CheckBox1.CheckState = CheckState.Indeterminate
        Label1Check()
    End Sub

    Sub Label1Check()
        If CheckBox1.Checked = True Then
            Label1.Text = "تم تدقيق هذا اليوم"
        Else
            Label1.Text = "يوم عطلة"
        End If
    End Sub

End Class