sound distortion and drop outs

[Bob de Celle]

I'm writing a string piece using a full compliment of strings with some divisis in the 2nds, violas and cellos. The orchesration isn't thick but it is full. I'm notating it in Finale 2004. I've written 24 bars but when I get past that, I have all kinds of distortion and the playack just stops.
Each section has it's own channel. I've never had this problem before with pieces five time larger than this. I hope someone can tell me what is going on because I can't fiure it out. All other programs are working fine. My sequencer and and audio files I have in Sound forge or Adobe Audition all playback normally. Thanks in advance.
Bob De Celle