Problem OccurredObject reference not set to an instance of an object

I am trying to split the function IPlookup in to two separate functions. The splitting of the functions is an attempt to reduce the amount of times the application has to go to the database by populating a datatable and selecting information from it.  This approach was suggested as a performance enhancement in a post I made for suggestions on performance enhancements. Please see the URL below for questions:

https://www.experts-exchange.com/questions/21784599/Performance-Improvements.html

I attempted several different approaches, but am still struggling to make it work.

I’m getting an error “Problem OccurredObject reference not set to an instance of an object.”

Original code:
     
Public Function IPLookup(ByVal DottedIP As String) As String
        Dim lngIP As Long
        Dim strCountry As String
        Dim con As New OleDbConnection
        Dim dtm As DataTableMapping
        Dim da As New OleDbDataAdapter
        Dim cmdSelect As New OleDbCommand
        Dim ds As New DataSet
        Dim dt As DataTable

        lngIP = Dot2LongIP(DottedIP)
        con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = C:\resource\master.mdb"
        dtm = da.TableMappings.Add("Table", "Country")
        cmdSelect.CommandText = "SELECT countryname FROM Country WHERE " & lngIP.ToString & " >= ipl1 and " _
                   & lngIP.ToString & "  <= ipl2"

        cmdSelect.Connection = con
        da.SelectCommand = cmdSelect
        da.Fill(ds)
        dt = ds.Tables("Country")
        If dt.Rows.Count = 0 Then
            strCountry = "Not is Database!"
        Else
            strCountry = dt.Rows(0).Item("countryname")
        End If

        Return strCountry
    End Function
End Class

Split code


Partial code (I included this partial code section because I wasn't sure if this was what was causing the error)

If (inFile.Length > 0) Then
            If (outFile.Length > 0) Then
                CountryDatatable() 'I added call to the datatable
                ConvertFiles(inFile, outFile)
                'Wave.Play("C:\resource\sounds\completed.wav")
                MsgBox("File Complete!")
            Else

Here is the modified code:

    Public Function CountryDatatable()
        Dim cmdSelect As New OleDbCommand
        Dim dtm As DataTableMapping
        Dim da As New OleDbDataAdapter
        Dim ds As New DataSet
        Dim dt As New DataTable
        Dim con As New OleDbConnection

        con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = C:\resource\master.mdb"
        cmdSelect.CommandText = "SELECT * from Country"
        dtm = da.TableMappings.Add("Table", "Country")
        cmdSelect.Connection = con
        da.SelectCommand = cmdSelect
        da.Fill(ds)
        dt = ds.Tables("Country")

    End Function

    Public Function IPLookup(ByVal DottedIP As String) As String
        Dim lngIP As Long
        Dim strCountry As String
        Dim ds As DataSet
        Dim dt As DataTable

        dt = ds.Tables("Country")
        lngIP = Dot2LongIP(DottedIP)
        Dim sql As String
        Dim foundrows() As DataRow
        sql = lngIP.ToString & ">=ipl1 and " & lngIP.ToString & " <= ipl2"
        foundrows = dt.Select(sql)

        If foundrows.Length = 0 Then
            strCountry = "unknown"

        Else
            strCountry = foundrows(0).Item("countryname")
        End If
        Return strCountry
    End Function


Thank you very much for your time and expertise,
Gr8life