Sorry - I always keep a single layer with a single instance of Dim Pro. So, if I have to layer things up, I do it with multiple instances of Dim Pro, each having one instrument, and I either clone midi data for layers, or I record multiple midi tracks at the same time.
This allows me to additionally do all of my levels in Sonar, rather than in Dim Pro, AND, many times strings/piano do have different voicing and sustain values, so for me I just keep it all separated individually.
Can you break your layers down into multiple Dim Pro and midi track instances? I never crash doing things as I have indicated above.
Bob Bone