Autocomplete Ajax.ASP.Net not response

I have code Webservice like this :
    Dim db As New MajorService()
    Dim dset As New System.Data.DataSet()

    <WebMethod()> _

    Public Function GetCompletionList(ByVal prefixText As String) As String()
        Dim totalRec As Integer
        Dim items As New List(Of String)
        db.thisDbName = "DatabaseSP"
        dset = db.RetrieveData("SELECT * FROM ref_user WHERE nama_lengkap '%" & prefixText & "%'")
        totalRec = dset.Tables("Recordset").Rows.Count
        For i As Integer = 1 To dset.Tables("Recordset").Rows.Count
       &n ...