HttpWebRequest. Ошибка при добавлении заголовков

Private headers As New Net.WebHeaderCollection
 
    Public Sub New()
        With headers
            '.Add("Accept: text/html, application/xhtml+xml, */*")
            .Add("Accept-Language: ru-RU")
            .Add("User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)")
            .Add("UA-CPU: AMD64")
        End With
    End Sub
 
    Public Function GETreq(ByVal url As String, Optional ByVal proxy As Net.WebProxy = Nothing) As String
        Dim out As String = ""
        Try
            Dim reqGET As System.Net.HttpWebRequest = System.Net.WebRequest.Create(url)
            If Not cooks Is Nothing Then reqGET.CookieContainer = cooks 
            For Each s As String In headers
                Dim h As String = s & ": " & headers.Get(s)
                reqGET.Headers.Add(s, headers.Get(s)) 'на этой строчке при добавлении Accept и User-Agent'а происходит исключение
            Next
            Dim resp As System.Net.HttpWebResponse = reqGET.GetResponse()
            cooks = New Net.CookieContainer
            For Each c As Net.Cookie In resp.Cookies
                cooks.Add(c)
            Next
            Dim stream As System.IO.Stream = resp.GetResponseStream()
            Dim sr As New System.IO.StreamReader(stream)
            out = sr.ReadToEnd()
        Catch ex As Exception
 
        End Try
        Return out
    End Function

Dim request As HttpWebRequest = WebRequest.Create(Args(0))
request.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:35.0) Gecko/20100101 Firefox/35.0"