VB error "expression is not a method" etc

[Danny Treart]

Having an issue in the Do While loop in the calculate total button. I'm getting these three errors, all pointing to "intCounter--"

Any ideas?

Expression is not a method.
Method arguments must be enclosed in parenthesis.
Expression expected.

Public Class Form1

    Private Sub btnAddWorkshop_Click(sender As Object, e As EventArgs) Handles btnAddWorkshop.Click
        'LODGING COSTS per city'
        Const dblAUSTIN_COST As Double = 95.0
        Const dblCHICAGO_COST As Double = 125.0
        Const dblDALLAS_COST As Double = 110.0
        Const dblORLANDO_COST As Double = 100.0
        Const dblPHOENIX_COST As Double = 92.0
        Const dblRALEIGH_COST As Double = 90.0
        Dim dblWorkshopCost As Double = 0.0

        Dim dblRegCost As Double = 0.0
        Dim dblLodgingDays As Double = 0.0
        Dim strFormattedPrice As String = ""

        If lstWorkshop.SelectedIndex < 0 Then 'No workshop selected...
            MessageBox.Show("Please select a workshop.")
            lstCosts.Items.Clear()
            lstLoc.SelectedIndex = -1
            lstWorkshop.SelectedIndex = -1
        ElseIf lstWorkshop.SelectedIndex = 0 Then 'Handling Stress Workshop - 3 Days long/ $595 Reg Fee
            dblRegCost = 595.0
            dblLodgingDays = 3.0
        ElseIf lstWorkshop.SelectedIndex = 1 Then 'Time MGMT Workshop - 3 Days long/ $695 Reg Fee
            dblRegCost = 695.0
            dblLodgingDays = 3.0
        ElseIf lstWorkshop.SelectedIndex = 2 Then 'Supervision Skills Workshop - 3 Days long/ $995 Reg Fee
            dblRegCost = 995.0
            dblLodgingDays = 3.0
        ElseIf lstWorkshop.SelectedIndex = 3 Then 'Negotiation Workshop - 5 Days long/ $1,295 Reg Fee
            dblRegCost = 1295.0
            dblLodgingDays = 5.0
        ElseIf lstWorkshop.SelectedIndex = 4 Then 'How to Interview Workshop - 1 Day long/ $395 Reg Fee
            dblRegCost = 395.0
            dblLodgingDays = 1.0
        End If

        If lstLoc.SelectedIndex < 0 Then
            MessageBox.Show("Please select a location.")
            lstCosts.Items.Clear()
            lstLoc.SelectedIndex = -1
            lstWorkshop.SelectedIndex = -1
        ElseIf lstLoc.SelectedIndex = 0 Then 'Austin Lodging
            dblWorkshopCost = (dblAUSTIN_COST * dblLodgingDays) + dblRegCost
        ElseIf lstLoc.SelectedIndex = 1 Then 'Chicago Lodging
            dblWorkshopCost = (dblCHICAGO_COST * dblLodgingDays) + dblRegCost
        ElseIf lstLoc.SelectedIndex = 2 Then 'Dallas Lodging
            dblWorkshopCost = (dblDALLAS_COST * dblLodgingDays) + dblRegCost
        ElseIf lstLoc.SelectedIndex = 3 Then 'Orlando Lodging
            dblWorkshopCost = (dblORLANDO_COST * dblLodgingDays) + dblRegCost
        ElseIf lstLoc.SelectedIndex = 4 Then 'Phoenix Lodging
            dblWorkshopCost = (dblPHOENIX_COST * dblLodgingDays) + dblRegCost
        ElseIf lstLoc.SelectedIndex = 5 Then 'Raleigh Lodging
            dblWorkshopCost = (dblRALEIGH_COST * dblLodgingDays) + dblRegCost
        End If

        If dblWorkshopCost <> 0 Then
            strFormattedPrice = dblWorkshopCost.ToString("c")
            lstCosts.Items.Insert(0, strFormattedPrice)
        End If


    End Sub

    Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
        Me.Close()
    End Sub

    Private Sub btnReset_Click(sender As Object, e As EventArgs) Handles btnReset.Click
        lstCosts.Items.Clear()
        lstLoc.SelectedIndex = -1
        lstWorkshop.SelectedIndex = -1
        txtTotalCost.Clear()

    End Sub

    Private Sub btnCalcTotal_Click(sender As Object, e As EventArgs) Handles btnCalcTotal.Click
        Dim intCounter As Integer = lstCosts.Items.Count
        Dim dblTotalCost As Double = 0
        Dim dblPrice As Double = 0
        Do While intCounter > 0
            dblPrice = CDbl(lstCosts.Items(intCounter))
            dblTotalCost += dblPrice
            intCounter--
        Loop
        Dim strTotalCostOutput = dblTotalCost.ToString("c")
        txtTotalCost.Text = strTotalCostOutput
    End Sub
End Class

[EDIT**]Changing it to...

intCounter -= 1

actually let me compile it, but I'm still having a few errors.

InvalidArgument=Value of '2' is not valid for 'index'.