Hey guys,

I'm sure this is in the wrong section, I don't know where to put it, I'm sorry.

So I'm making program that calculates the cost of a call based on data inputted, but I am have a major problem, I keep getting an error saying "Conversion from string "" to type 'Double' is not valid."

I have been searching for days and I understand the problem, that I cannot convert an empty string to a double, but what do I do?

Here is the code:
Code:
Public Class Form1

    Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lblAccountLabel.Click

    End Sub

    Private Sub Label1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lblTelephoneLabel.Click

    End Sub

    Private Sub Label5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lblBasic.Click

    End Sub

    Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
        Dim iAccount As Integer
        Dim sTelephone As String
        Dim sPlan As String
        Dim iDuration As Integer
        Dim dDate As Date
        Dim dCountry As Double
        Dim iTime As Integer
        Dim bEvening As Boolean
        Dim dFlagfall As Double
        Dim dBasic As Double
        Dim dPlanDisc As Double
        Dim dLoyalty As Double
        Dim dTotal As Double
        Dim dGST As Double

        'Determines Flagfall by inputted plan
        sPlan = txtPlan.Text
        
        dFlagfall = CDbl(lblFlagfall.Text) <-- IT POINTS TO THIS WITH THE ERROR

        If sPlan = "No Plan" Then
            dFlagfall = 2.0
        ElseIf sPlan = "Bronze" Then
            dFlagfall = 1.5
        ElseIf sPlan = "Silver" Then
            dFlagfall = 0.75
        ElseIf sPlan = "Gold" Then
            dFlagfall = 0.25
        Else
            MsgBox("Unknown Plan")
        End If

        'Calculates rate per minute by inputted country
        dCountry = CDbl(lblCountry.Text)

        If txtCountry.Text = "Japan" Then
            dCountry = 0.34
        ElseIf txtCountry.Text = "China" Then
            dCountry = 0.86
        ElseIf txtCountry.Text = "India" Then
            dCountry = 0.78
        ElseIf txtCountry.Text = "UK" Then
            dCountry = 0.37
        ElseIf txtCountry.Text = "USA" Then
            dCountry = 0.42
        ElseIf txtCountry.Text = "Canada" Then
            dCountry = 0.56
        ElseIf txtCountry.Text = "Indonesia" Then
            dCountry = 0.38
        ElseIf txtCountry.Text = "New Zealand" Then
            dCountry = 0.22
        ElseIf txtCountry.Text = "Other" Then
            dCountry = 1.1
        End If

        'Displays inputted plan for summary reasons
        lblPlan.Text = sPlan

        'Calculates basic cost then displays
        txtDuration.Text = lblDuration.Text
        iDuration = lblDuration.Text
        dBasic = lblBasic.Text

        dBasic = dFlagfall + (iDuration * dCountry)

        'Displays Plan Discount
        dPlanDisc = CDbl(lblPlanDiscount.Text)
        If sPlan = "No Plan" Then
            dPlanDisc = 0
        ElseIf sPlan = "Bronze" Then
            dPlanDisc = 0.05
        ElseIf sPlan = "Silver" Then
            dPlanDisc = 0.1
        ElseIf sPlan = "Gold" Then
            dPlanDisc = 0.15
        Else
            MsgBox("Unknown Plan")

        End If

        'Calculates and displays Loyalty discount
        dLoyalty = CDbl(lblLoyalty.Text)

        dLoyalty = iTime * 0.02

        'Calculates and displays total cost




    End Sub

    Private Sub lblFlagfall_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lblFlagfall.Click

    End Sub
End Class
Any help would be so greatly appreciated and hopefully mods move this to it's correct location.

Thank you.