Немогу понять в чём дело??? - VB

Dim x As Double, y As Double, k As Double, z As Double
 
Private Sub Cmd1_Click()
If IsNumeric(Txt1) = True And IsNumeric(Txt2) = True And IsNumeric(Txt3) = True Then
x = Txt1.Text
k = Txt2.Text
z = Txt3.Text
    If x > 0 Then y = (x + k) / (5 + (Sin(z)) ^ 2)
    ElseIf x <= 0 Then y = Sqr(Abs(k + (Tan(z)) ^ 2))
Txt4.Text = y
  Else
    MsgBox "Ошибка ввода данных", vbCritical, "Сообшение"
    Exit Sub
    End If
End Sub
 
Private Sub Cmd2_Click()
End
End Sub