新人求助~一个调用过程的问题!到底哪里不对呀摔!!

Public Class Form1
    Sub maxlength(ByVal s$, ByRef max$)
        Dim n$, i%
        s = LTrim(s)
        i = InStr(s, " ")

        Do While i <> 0

            n = Mid(s, 1, i - 1)
            If Len(n) < Len(max) Then max = n
            s = Mid(s, i + 1)
            i = InStr(s, " ")

        Loop
        If Len(s) > Len(max) Then max = s
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim s, m As String
        s = TextBox1.Text

        Call maxlength(s, m)
        TextBox2.Text = m
    End Sub
End Class