Insert a row inro an existing dataset

I have a dataset retrieved from a database and need to add a row to it under certain conditions. I have the code:-
Try
            With Me.DStrn.Tables("Transactions")
                For Each DR In .Rows
                    If DR.Item("XactType") = 3 And DR.Item("VatDiscAmt") <> 0 Then
                        HoldDisc = DR.Item("VatDiscAmt")
                        DR = DStrn.Tables("Transactions").NewRow
                        DR("AlphType") = "Disc."
                        DR("TotalPosting") = HoldDisc
                        DR("TrnId") = 0
                        DR("InvSource") = ""
                        DR("XactDate") = Today
                        DR("XactType") = 0
                        DR("XactStatus") = 0
                        DR("OurRef") = ""
                        DR("YourRef") = ""
                        DR("LoadCard") = ""
                        DR("PaymtDueDate") = Today
                        DR("AlphType") = ""
                        DR("NonDiscTotal") = HoldDisc
                        DR("RunningBal") = -99999999.99
                        DR("AmountAllocated") = 0
                        DR("VatDiscAmt") = 0
                        DStrn.Tables("Transactions").Rows.InsertAt(DR, 0)
                       
                    End If
                Next
            End With
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

his comes up with an exception message "Collection was Modified; enumeration operation might not execute and bombs me out,

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