Object Reference Not Set To An Instance Of An Object Error

I'm new to ASP.Net and am trying to pull data from the db and populate an excel spreadsheet. I kget this error:
Object reference not set to an instance of an object.
on this:
line 55: For i = 0 To dr.FieldCount - 1
Here is my code:

Protected Sub On_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Submit.Click
        Dim i As Integer
        Dim strLine As String, filePath, fileName, fileExcel
        Dim objFileStream As FileStream
        Dim objStreamWriter As StreamWriter
        Dim nRandom As Random = New Random(DateTime.Now.Millisecond)
        Dim Location As String
        Dim SDate As String
        Dim EDate As String

        Location = Request.QueryString("Location")
        SDate = Request.QueryString("StartDate")
        EDate = Request.QueryString("EndDate")

        'Dim fs As Object, myFile As Object
        Dim cnn As SqlConnection = New SqlConnection("server=**.**.**.**;uid=******;pwd=******database=***")
        'Create a pseudo-random file name.
        fileExcel = "NR_Report" & nRandom.Next().ToString() & ".xls"
        'Set a virtual folder to save the file.
        'Make sure that you change the application name to match your folder.
        filePath = "********"
        fileName = filePath & "" & fileExcel
        'Use FileStream to create the .xls file.
        objFileStream = New FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write)
        objStreamWriter = New StreamWriter(objFileStream)
        'Use a DataReader to connect to the Pubs database.
        cnn.Open()
        Dim sql As String = "select [Tech Number] = u.user_techNo, Team = u.user_team, Name = upper(u.user_firstName) + ' ' + upper(u.user_lastName), [Total Jobs] = SUM(nr.nr_totaljobs), [Total IRDs] = SUM(nr.nr_totalirds), [IRDs Connected] = SUM(nr.nr_irdsConnected), [IRDs Non-Responding] = SUM(nr.nr_irdsNonResponding), [Percent Non-Responding] = case when SUM(nr.nr_irdsNonResponding) = 0 then 0.00 else round(SUM(cast(nr.nr_irdsNonResponding as decimal) ) / SUM(cast(nr.nr_irdsConnected as decimal)) * 100.00, 2) end from tblUsers u , tblNonResponders nr where u.user_techNo = nr.nr_irtech and u.user_techNo is not null and u.user_team is not null and u.user_office = " & Location & " and u.user_fireDate is null and u.user_suspend is null and nr.nr_reportweek between " & SDate & " and " & EDate & " group by u.user_techno, u.user_firstName, u.user_lastName, u.user_team order by u.user_team"
        Dim cmd As SqlCommand = New SqlCommand(sql, cnn)
        Dim dr As SqlDataReader
        'Try
        'dr = cmd.ExecuteReader()
        'Catch ex As SqlException
        'Response.Write(ex.Message)
        'End Try
        'Enumerate the field names and records that are used to build the file.

        For i = 0 To dr.FieldCount - 1
            strLine = strLine & dr.GetName(i).ToString & Chr(9)
        Next
        'Write the field name information to file.
        objStreamWriter.WriteLine(strLine)
        'Reinitialize the string for data.
        strLine = ""
        'Enumerate the database that is used to populate the file.
        While dr.Read()
            For i = 0 To dr.FieldCount - 1
                strLine = strLine & dr.GetValue(i) & Chr(9)
            Next
            objStreamWriter.WriteLine(strLine)
            strLine = ""
        End While
        'Clean up.
        dr.Close()
        cnn.Close()
        objStreamWriter.Close()
        objFileStream.Close()
    End Sub

Thanks in advance for any help.