Ошибка в программном коде - VB

Private Sub cmdrun_Click()
Dim x As Single
Dim e As Single
Dim S As Single
Dim y As Single
Dim n As Integer
x = CSng(txtx.Text)
e = CSng(txte.Text)
S = 0
n = 0
y = x
Do While Abs(y) > e
S = S + y
n = n + 1
y = y * (-((x ^ 4) / ((2 * n - 1) * (2 * n) * (4 * n - 2) * (4 * n - 1) * (4 * n) * (4 * n + 1))))
Loop
txts.Text = CStr(S)
txtn.Text = CStr(n)
End Sub