the issue we were having was that the period should be closed for our AP/AR team but our accountants still need to post advanced intercompany journals, which Netsuite treats as AP/AR transactions...(and they are, technically...)
You can try to get around this by instead adjusting the AP/AR forms to make period non-selectable and having it default but we had mixed results with that approach. And one or two exceptions is all it takes to make an angry accountant