A mature song won't record anymore tracks although the appropriate record lights show. Other songs record ok

A 16 track song of mine won't allow recording of anymore tracks, although the appropriate record lights show correctly. The cursor moves but no yellow recording strip appears. If I remove tracks it will still not record. Other songs record ok. This is the second song to suffer from this recently. Before this week I have not had this problem. Performance monitor fine. Record max indicator shows 7:21 days. when arming a track it then shows 15:18 days

I have an Audiobox 44vsl (v1.05) Studio ! version 3.5.2.44603

PC: Acer Aspire GX781 8GB Ram i5 7400 processor Windows 10 OS