Помогите исправить ошибку в коде - VB

Private Sub cmdCalculate_Click()
    Dim Principal As Currency
    Dim InterestRate As Double
    Dim InterestEarned As Currency
    Dim FutureValue As Currency
    Dim RatePerPeriod As Double
    Dim Periods As Integer
    Dim CompoundType As Integer
    Dim i As Double
    Dim n As Integer
    
    Principal = (txtPrincipal.Text)
    InterestRate = CDbl(txtInterestRate.Text) / 100
    
    If optMonthly.Value = True Then
        CompoundType = 12
    ElseIf optQuarterly.Value = True Then
        CompoundType = 4
    ElseIf optSemiannually.Value = True Then
        CompoundType = 2
    Else
        CompoundType = 1
    End If
    
    Periods = CInt(txtPeriods.Text)
    i = InterestRate / CompoundType
    n = CompoundType * Periods
    RatePerPeriod = InterestRate / Periods
    FutureValue = Principal * ((1 + i) ^ n)
    InterestEarned = FutureValue - Principal
    
    txtInterestEarned.Text = FormatCurrency(InterestEarned)
    txtAmountEarned.Text = FormatCurrency(FutureValue)
End Sub