The settings for Credit Limit Checking in AR Options are to use either the defined credit limit or the age of invoices on the A/R Aging, or to use both. It does not look at closed sales orders.  It will include open sales orders if you select the checkbox to include them.

Thank you for your quick response, but unfortunately, that is not true in my system. I intentionally placed the limit of this one customer at open invoices + open sales orders, but I still get the credit limit exceeded message. There are closed sales orders listed on the S/O tab of this customer. When I set the credit limit to include those, the message goes away. I have checked the A/R Options, but it only gives a box to check to include Open S/Os. I didn't see an option related to Closed S/Os. Have you had this happen?