VB 2005 - Windows Vista

I have a form that seems to lock up when the number of rows exceed the
height of the datagridview.  The following code executes when data is
received through the serial port (ie. barcode scanning).  It seems that
everything works GREAT and processes as it was meant to be until the rows
exceed the display area.  I have 7 columns.  The Description column is the
only column with the AutoSizeMode set to Fill.  The datagridview is docked
to the top.  DataSource and DataMember for the DGV is not set to any
dataset.

I have the vertical scrollbar property set but it does not show up most of
the time.  When/If it does, when I try and utilize the scrollbar, it locks
up the application immediately.  I don't understand but I think it has to do
with the following method.

Sub ReceiveData(ByVal msg As String)        'Called after serial port has
received data and trimmed the value
       CheckForIllegalCrossThreadCalls = False
       description = Nothing        'form instance variable
       loc = Nothing
       Dim cmmInvMan As OleDbCommand
       Dim strSQL As String
       Dim drdTest As OleDbDataReader
       Dim cnnInvMan As OleDbConnection = New
OleDbConnection(My.Settings.Inventory_management_databaseConnectionString)
       cnnInvMan.Open()

       strSQL = "SELECT * FROM Products WHERE ProductIDNumber = '" & msg &
"'"
       cmmInvMan = New OleDbCommand(strSQL, cnnInvMan)
       drdTest = cmmInvMan.ExecuteReader
       Do While drdTest.Read
           prodIDNum = CInt(drdTest.Item("ProductID"))
           description = drdTest.Item("ProductDescription").ToString
           loc = drdTest.Item("ProductLocation").ToString
           minimumOnHand = CInt(drdTest.Item("ReorderLevel"))
           maximumOnHand = CInt(drdTest.Item("MinimumRequired"))
       Loop

       drdTest.Close()

       strSQL = "SELECT SUM(UnitsReceived) - SUM(UnitsSold) -
SUM(UnitsShrinkage) AS UnitsOnHand " & _
               "FROM [" &
Me.Inventory_management_databaseDataSet.Inventory_Transactions.TableName &
"] WHERE (ProductID = " & prodIDNum & ")"

       cmmInvMan = New OleDbCommand(strSQL, cnnInvMan)
       drdTest = cmmInvMan.ExecuteReader
       Do While drdTest.Read
           Try
               units = CInt(drdTest.Item("UnitsOnHand"))
           Catch ex As InvalidCastException
               units = 0
           End Try
       Loop

       drdTest.Close()
       cnnInvMan.Close()

       Dim value As Integer
       Dim duplicateRow As DataGridViewRow

       For Each duplicateRow In Me.DataGridView1.Rows
           If duplicateRow.Cells(0).Value Is Nothing Then Exit For
           If duplicateRow.Cells(0).Value.ToString = msg Then
               'MessageBox.Show(duplicateRow.Cells(1).ToString)
               value = CInt(duplicateRow.Cells(4).Value)
               value += 1
               duplicateRow.Cells(4).Value = value.ToString
'unitsScanned
               If duplicateRow.Cells(1).Value Is Nothing Then  'description
column
                   duplicateRow.Cells(1).Value = description
               End If
               If duplicateRow.Cells(3).Value Is Nothing Then  'UnitsOnHand
                   duplicateRow.Cells(3).Value = units.ToString
               End If
               If duplicateRow.Cells(2).Value Is Nothing Then   'location
                   duplicateRow.Cells(2).Value = loc
               End If
               If duplicateRow.Cells(5).Value Is Nothing Then  'minOnHand
                   duplicateRow.Cells(5).Value = minimumOnHand.ToString
               End If
               If duplicateRow.Cells(6).Value Is Nothing Then   'maxOnHand
                   duplicateRow.Cells(6).Value = maximumOnHand.ToString
               End If
               Exit Sub
           End If
       Next

       Dim row As String() = {msg, description, loc, units.ToString, "1",
minimumOnHand.ToString, maximumOnHand.ToString}
       Me.DataGridView1.Rows.Add(row)
End Sub

TIA,
Tony K.