Im just curious what is wrong in my code, when i click the void button an error is shown, but it runs smoothly when the void button is not click. Here is my code, thanks for your help guys!

Public Class Pizza
    Private Sub rdPrimo_CheckedChanged(sender As Object, e As EventArgs) Handles rdPrimo.CheckedChanged
        If rdPrimo.Checked = True Then
            cbBacon.Checked = True
            cbCheese.Checked = True
            cbGroundBeef.Checked = False
            cbMushroom.Checked = False
            cbOnion.Checked = True
            cbPepper.Checked = False
            cbSalami.Checked = False
            cbTomato.Checked = False
            txtPizza.Text = "Primo"
            txtPrice.Text = "185"
            txtQty.Text = "1"
            txtVat.Text = (".12")
            Convert.ToDouble(txtPrice.Text)
            Convert.ToDouble(txtVat.Text)
            txtVat.Text = txtPrice.Text * 0.12
            txtTotal.Text = Val(txtPrice.Text)
        End If
    End Sub

    Private Sub rdSpecial_CheckedChanged(sender As Object, e As EventArgs) Handles rdSpecial.CheckedChanged
        If rdSpecial.Checked = True Then
            cbBacon.Checked = True
            cbCheese.Checked = True
            cbGroundBeef.Checked = False
            cbMushroom.Checked = False
            cbOnion.Checked = True
            cbPepper.Checked = True
            cbSalami.Checked = False
            cbTomato.Checked = False
            txtPizza.Text = "Special"
            txtPrice.Text = "250"
            Convert.ToDouble(txtPrice.Text)
            Convert.ToDouble(txtVat.Text)
            txtVat.Text = txtPrice.Text * 0.12
            txtTotal.Text = Val(txtPrice.Text)
        End If
    End Sub
    Private Sub rdDeluxe_CheckedChanged(sender As Object, e As EventArgs) Handles rdDeluxe.CheckedChanged
        If rdDeluxe.Checked = True Then
            cbBacon.Checked = True
            cbCheese.Checked = True
            cbGroundBeef.Checked = True
            cbMushroom.Checked = True
            cbOnion.Checked = True
            cbPepper.Checked = True
            cbSalami.Checked = True
            cbTomato.Checked = True
            txtPizza.Text = "Deluxe"
            txtPrice.Text = "300"
            Convert.ToDouble(txtPrice.Text)
            Convert.ToDouble(txtVat.Text)
            txtVat.Text = txtPrice.Text * 0.12
            txtTotal.Text = Val(txtPrice.Text)
        End If
    End Sub



    Private Sub btnClose_Click(sender As Object, e As EventArgs) Handles btnClose.Click
        Me.Close()
        MsgBox("Thank You!")
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnVoid.Click
        cbBacon.Checked = False
        cbCheese.Checked = False
        cbGroundBeef.Checked = False
        cbMushroom.Checked = False
        cbOnion.Checked = False
        cbPepper.Checked = False
        cbSalami.Checked = False
        cbTomato.Checked = False
        txtPizza.Text = ""
        txtPrice.Text = ""
        txtVat.Text = ""
        rdPrimo.Checked = False
        rdSpecial.Checked = False
        rdDeluxe.Checked = False
        txtQty.Text = ""
        txtTotal.Text = ""
        txtAmount.Text = ""
        txtChange.Text = ""
    End Sub
    Dim origvalue As Double
    Dim neworder As Double
    Dim newval
    Dim newprice

    Private Sub txtVat_onChanged(sender As Object, e As EventArgs) Handles txtVat.TextChanged
        If txtQty.Text = "" Then Exit Sub
        If (Val(txtQty.Text) >= 1) Then
            origvalue = Double.Parse(txtPrice.Text)
            neworder = Double.Parse(txtQty.Text)

            newval = origvalue * (neworder)
            newprice = newval.ToString()
        End If
    End Sub

    Private Sub btnEnter_Click(sender As Object, e As EventArgs) Handles btnEnter.Click
        txtTotal.Text = Val(txtPrice.Text) * Double.Parse(Val(txtQty.Text))
        txtVat.Text = Val(txtVat.Text) * Double.Parse(txtQty.Text)
        btnEnter.Visible = False
    End Sub

    Private Sub txtQty_onChanged(sender As Object, e As EventArgs) Handles txtQty.TextChanged
        If txtQty.Text > 1 Then
            btnEnter.Show()
        Else
            btnEnter.Hide()
        End If
    End Sub

    Private Sub txtAmount_onChanged(sender As Object, e As EventArgs) Handles txtAmount.TextChanged
        If txtAmount.Text > txtTotal.Text Then
            btnenter1.Show()
        Else
            MsgBox("Insufficient Amount!")
            btnenter1.Hide()
        End If
    End Sub

    Private Sub btnenter1_Click(sender As Object, e As EventArgs) Handles btnenter1.Click
        txtChange.Text = Val(txtAmount.Text) - Val(txtTotal.Text)
        btnenter1.Visible = False
    End Sub

End Class

the event of the controls were triggered when you changed their values. Try to remove their handler first before changing the values of your controls then put back the handlers once done.

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