Mainstage seems unstable please help

I have recently downloaded Mainstage 2.2.2 on a macbook pro running osx 10.6.8 with a 2.53 intel core 2 duo and 4gb ram. I also downloaded all the jampacks. The first couple of days of messing with it seemed to go ok but now everytime i start it up and load a concert, I can only get a couple of minutes normal audio before the audio goes into some horendous distortion. I also have had issues early on of "unexpected shutdowns" while working in the layout screen building a mixer. I should probably add that I am using a presonus firestudio project as the input. My idea was to use Mainstage as a travel rig for backing up my wife (vocalist) with guitar and keys. I starting to feel as if this idea was too good to be true. I have done this several times before using GB but liked the idea of having a all in one interface to work through. I'm hoping someone can tell me what I'm doing wrong so that this program becomes stable.