I recently had this exact problem with a customer on 4.50. It took quite awhile to troubleshoot, but it was due to a printer problem. One of the things the client did was turn off and then turn on the printer which resolved the problem for the time being, but they eventually replaced it as it was a problem on and off. On a side note, the sales order did not save in the open file, as you reported, but it was in the Sales Order History file as ""Active"".