DataGridView throwing null reference error after code update - vb.net

Question

As a fairly new user to VB.NET, I thought it was about time I tried to get to grips with DataGridView after learning the fundamentals of ListView and other basic knowledge. However, I have an error of 'Object reference not set to an instance of an object'. Let me try to explain how I think I have created this error but cannot seem to find a way out.
Initially, I had the code in the 1 winform, DGVtest.vb and upon pressing the 'fill grid' button, it filled the grid nulls and all. What I thought I would do to keep the code cleaner and in the long term, have more control, is to move the code out of DGVtest.vb and create a module, DGVmod.vb and put the code in there. However, being a new user, I now find myself totally out of my depth and looking for assistance as to how to move forward with this.
So, to outline, the DGV is in DGVtest.vb with a 'fill grid' button which calls 'DGVmod.fillgrid()' to fill the grid. If anyone can offer any assistance, I will be very grateful. Many thanks
Imports System
Imports System.Data
Imports System.Data.OleDb
Module DGVmod
Private da As OleDbDataAdapter
Private ds As DataSet
Public dtSource As DataTable
Private PageCount As Integer
Private maxRec As Integer
Private pageSize As Integer
Private currentPage As Integer
Private recNo As Integer
Sub fillPostings()
Dim conn As OleDbConnection = New OleDbConnection(My.Settings.storageConnectionString)
'Set the DataAdapter's query.
da = New OleDbDataAdapter("select * from Postings", conn)
ds = New DataSet()
' Fill the DataSet.
da.FillSchema(ds, SchemaType.Source, "Postings")
da.Fill(ds, "Postings")
' Set the source table.
dtSource = ds.Tables("Postings")
End Sub
Sub btnprevious()
If Not CheckFillButton() Then Return
If currentPage = PageCount Then
recNo = pageSize * (currentPage - 2)
End If
currentPage = currentPage - 1
'Check if you are already at the first page.
If currentPage < 1 Then
MessageBox.Show("You are at the First Page!")
currentPage = 1
Return
Else
recNo = pageSize * (currentPage - 1)
End If
loadpages()
End Sub
Sub btnnext()
'If the user did not click the "Fill Grid" button then Return
If Not CheckFillButton() Then Return
'Check if the user clicked the "Fill Grid" button.
If pageSize = 0 Then
MessageBox.Show("Set the Page Size, and then click the ""Fill Grid"" button!")
Return
End If
currentPage = currentPage + 1
If currentPage > PageCount Then
currentPage = PageCount
'Check if you are already at the last page.
If recNo = maxRec Then
MessageBox.Show("You are at the Last Page!")
Return
End If
End If
loadpages()
End Sub
Sub btnlast()
If Not CheckFillButton() Then Return
' Check if you are already at the last page.
If recNo = maxRec Then
MessageBox.Show("You are at the Last Page!")
Return
End If
currentPage = PageCount
recNo = pageSize * (currentPage - 1)
loadpages()
End Sub
Private Sub DisplayPageInfo()
DGVtest.txtDisplayPageNo.Text = "Page " & currentPage.ToString & "/ " & PageCount.ToString
End Sub
Sub fillgrid()
Try
'Set the start and max records.
pageSize = CInt(DGVtest.cmbPageSize.Text)
maxRec = DGVtest.DGV.Rows.Count
PageCount = maxRec \ pageSize
' Adjust the page number if the last page contains a partial page.
If (maxRec Mod pageSize) > 0 Then
PageCount = PageCount + 1
End If
'Initial seeings
currentPage = 1
recNo = 0
' Display the content of the current page.
loadpages()
Catch ex As Exception
MessageBox.Show(ex.InnerException.ToString)
End Try
End Sub
Private Sub loadpages()
Dim i As Integer
Dim startRec As Integer
Dim endRec As Integer
Dim dtTemp As DataTable
'Dim dr As DataRow
'Duplicate or clone the source table to create the temporary table.
dtTemp = dtSource.Clone <--- ERROR IS HERE
If currentPage = PageCount Then
endRec = maxRec
Else
endRec = pageSize * currentPage
End If
startRec = recNo
'Copy the rows from the source table to fill the temporary table.
For i = startRec To endRec - 1
dtTemp.ImportRow(dtSource.Rows(i))
recNo = recNo + 1
Next
DGVtest.DGV.DataSource = dtTemp
DisplayPageInfo()
End Sub
Sub btnfirst()
If Not CheckFillButton() Then Return
' Check if you are already at the first page.
If currentPage = 1 Then
MessageBox.Show("You are at the First Page!")
Return
End If
currentPage = 1
recNo = 0
loadpages()
End Sub
Private Function CheckFillButton() As Boolean
'Check if the user clicks the "Fill Grid" button.
If pageSize = 0 Then
MessageBox.Show("Set the Page Size, and then click the ""Fill Grid"" button!")
CheckFillButton = False
Else
CheckFillButton = True
End If
End Function
Sub cmbpage()
'Set the start and max records.
pageSize = CInt(DGVtest.cmbPageSize.Text)
maxRec = dtSource.Rows.Count
PageCount = maxRec \ pageSize
' Adjust the page number if the last page contains a partial page.
If (maxRec Mod pageSize) > 0 Then
PageCount = PageCount + 1
End If
'Initial seeings
currentPage = 1
recNo = 0
' Display the content of the current page.
loadpages()
End Sub
End Module