I would look at their procedures.  How or why is more than one person getting invoicing information for the same sales order.

Well, obviously it's in her keystrokes, but of course she's not going to remember exactly how that one was different, but the real question is HOW does Sage let this happen?  I've tried as separate users at the same time, having one up on my screen at the same time, etc, but Sage correctly tells me each time that either the sales order is already in another record or the record is in use.