Client found response content type of '', but expected 'text/xml'.

I goet this error when trying to execute my SSRS reports.
Client found response content type of '', but expected 'text/xml'.
The request failed with an empty response.
VB Code:
Private Sub btnprint_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnprint.Click
        'RenderPDF()

        Dim rview As New Microsoft.Reporting.WebForms.ReportViewer()
        Dim apr As New AppSettingsReader()
        rview.ServerReport.ReportServerUrl = New Uri(apr.GetValue("ReportServer", GetType(String)))
        Dim paramList As New System.Collections.Generic.List(Of Microsoft.Reporting.WebForms.ReportParameter)()
        paramList.Add(New Microsoft.Reporting.WebForms.ReportParameter("@DateServed", RadDatePick.SelectedDate))
        paramList.Add(New Microsoft.Reporting.WebForms.ReportParameter("@Location", ddlSch.SelectedValue))
        paramList.Add(New Microsoft.Reporting.WebForms.ReportParameter("@MenuType", ddlmenutype.SelectedValue))

        rview.ServerReport.ReportPath = "/ReportFolder/ReportName"
        rview.ServerReport.SetParameters(paramList)

        Dim mimeType As String = Nothing
        Dim encoding As String = Nothing
        Dim extension As String = Nothing
        Dim deviceInfo As String = Nothing
        Dim streamIds As String() = Nothing
        Dim warnings As Microsoft.Reporting.WebForms.Warning() = Nothing
        Dim format As String = "PDF"

        deviceInfo = "<DeviceInfo>" + "<SimplePageHeaders>True</SimplePageHeaders>" + "</DeviceInfo>"
        Dim bytes As Byte() = rview.ServerReport.Render(format, deviceInfo, mimeType, encoding, extension, streamIds, warnings)
        Response.Clear()

        If format = "PDF" Then
            Response.ContentType = "application/pdf"
            Response.AddHeader("Content-disposition", "filename=output.pdf")
        End If

        Response.OutputStream.Write(bytes, 0, bytes.Length)
        Response.OutputStream.Flush()
        Response.OutputStream.Close()
        Response.Flush()
        Response.Close()
    End Sub