vb不认 Trim("aa")这样的语句咋回事？

我打开运行一个项目，报告can't find project or libary
然后定位在
Private Sub cmdRecieve_Click() '这行变黄
'    判断输入数据是否符合要求
    If Trim(txtIP1.Text) = "" Then  'Trim 被选变蓝
        MsgBox "IP地址不能为空！"
        txtIP1.SetFocus
        txtIP1.SelStart = 0
        txtIP1.SelLength = Len(txtIP1)
        Exit Sub
    Else
        strIP1 = Me.txtIP1.Text
    End If

    ......

End Sub