Invoice Number Generation

I started a small business and have created an accounting DB with advice from my accountant. In Part of my business I generate invoices for the same customers every month. I use a unique invoice number that helps with tracking etc. So I haven't been able to get an auto number to work. Currently, I dump the records in monthly then manually update the invoice number, but it is taking too much time now. I have been trying to adapt some code I found online but I am new to the coding end of Access. Most of the time I have been able to get things done with queries and macros. So this is the code that I am trying to adapt. Private Sub InvUDB_Click() Dim InvNo As DAO.Database Dim rstMInvoice As DAO.Recordset Dim rstInv1 As DAO.Recordset Set InvNo = CurrentDb Set rstMInvoice = InvNo.OpenRecordset("MInvoice") '**** This is the line that the debugger opens up to after the error Set rstInv1 = InvNo.OpenRecordset("Inv1") rstMInvoice.MoveFirst Do Until rstInvoice.EOF If rstMInvoice!Invoice = 0 Then rstMInvoice.Edit rstMInvoice!Invoice = rstInv1!Inv rstMInvoice.Update End If rstMInvoice.MoveNext DoCmd.SetWarnings False DoCmd.OpenQuery "Invoice_Q000" DoCmd.OpenQuery "Invoice_Q002" DoCmd.SetWarnings True Loop End Sub I get an error message 3167: > “You referred to a record that you deleted or that another user in a multiuser environment deleted. Move to another record, and then try the operation again.” When I Debug it highlights The following row: > Set rstMInvoice = InvNo.OpenRecordset("MInvoice") I use the two queries below this line to generate a temp table with the new invoice number, (Max Inv No for current year and Month Plus 1). I have tried running these queries in different places in the code with no luck. As you can see I do not have a clue as how to write this or how to get this code to run. When I replace everything past the equal sign with a constant it works but it replaces all the qualifying records with that constant. Can someone help me with this?