I had a similar thing happen, but with a much more basic project. Two recorded MIDI files and VSTis for each (on separate tracks). I forget the exact point that it locked up, but I'm about 95% sure it was when I tried to do something with one of the two VSTis. After opening the project again twice, and it locking up both times, I could see that it was locking up when it was loading a particular VSTi. What I did was open the .RPP file in Windows notepad, and took out the code for whichever track the VSTi was on, and voila, it worked again. I managed to salvage the MIDI by copying it to another track (in editinf the .RPP file), but that shouldn't be a problem for you if you're using audio. I would say it's probably a plugin problem. Cheers, Pembo.