I have created the following function
Public Sub NextInvoiceNo()
On Error Resume Next
If IsNull(DMax("InvoiceNo", "Invoice")) Then
Forms!F_Invoice!InvoiceNo = 1
Else
Forms!F_Invoice!InvoiceNo = DMax("InvoiceNo", "Invoice") + 1
End If
Forms!F_Invoice.Refresh
If Err = 3022 Then...