这几天刚开始学VB6，照着书写的小程序，可不知道怎么的出现语句错误，还请问各高人指点，不知道哪里出错了？

Private Sub cmdEvaluate_Click()
    'declare two floating point variables.
    Dim reWidth As Double, reLength As Double
    On Error GoTo wrongvalues
    'extract values from input textBox controls.
    reWidth = CDbl(txtWidth.Text)
    reLength = CDbl(txtLength.Text)
    Ensure that they are positive values.   '在插入这句后，为什么出现“缺少：语句结束”的错误
    If reWidth <= 0 Or reLength <= 0 Then GoTo wrongvalues
    'evaluate results and assign to output text boxes.
    txtPerimeter.Text = CStr((reWidth + reLength) * 2)
    txtArea.Text = CStr(reLength * reWidth)
    Exit Sub
wrongvalues:
    MsgBox "please enter valid Length and Width values", vbExclamation
End Sub

我是照着《visual Basic 6 编程技术大全》写的，后面的“'插入……”是我自己加的。