Strange No. eries Error Nav4.0/SQL

We have users on Nav4/SQL who are receiving the following error message with some regularity: The Sales Header does not exist. Document Type=‘Order’, No.=‘SQ10145’ Document Type: Order, No.:SQ10145 This message occurs when they try to enter a new sales order (Hit F3 on the sales order card) Now the SQ prefix tells me that for some reason Navision looked at the Sales Quote number series rather than the Sales Order number series. (This client does not use quotes at all - everything starts with the Sales Order) Since it used the wrong number series, I can understand why it is unable to find the sales header (Doc Type ‘Order’), but does anyone know how to prevent it from using the wrong No. Series in the first place? When they try a second time, they wind up with a “proper” sales order number and all is well. The client has about 8 people entering new sales orders, but generally in the neighborhood of 100 orders per day.