Help with unbounding a Grid

Hello,

I am loading my grid with code in Part A, but when trying to save data entered in code in Part B I receive the following error:

Not supported when the grid is bound

on line: For x As Integer = 0 To C1NSN.Rows.Count - 1

How do you unbound the grid or fix this error?

Part A:

 Dim NSN As New DataSet
        NSN.ReadXml(Application.StartupPath + "\App_Data\Blank.xml")
        C1NSN.DataSource = NSN.Tables(0)



Part B:

    For x As Integer = 0 To C1NSN.Rows.Count - 1
                If CheckForNSNFix.Contains(C1NSN.Rows(x).ToString) Then
                    For Each xnLink As Xml.XmlNode In xdNSN.SelectNodes("/Root/NSNTable[NSN='" & C1NSN.Rows(x).ToString & "']")
                        NSN_ID = xnLink.SelectSingleNode("NSN_ID").InnerText
                        If NSN_ID <> "" Then
                            CD = NSN_ID
                            If u > 0 Then
                                num1 = num1 & "" & CD & ","
                            Else
                                num1 = CD & ","
                            End If
                            u = u + 1
                        End If
                    Next
                End If
            Next