Check VST Performance bar, and see if your Hard Disk is running into the red. I've noticed that on my computer anything past 50% utilization is asking for trouble. Also, 256MB of ram really is a bare minimum. You should go to at least 512MB. If the HD is being hit a lot, you can increase the memory allocation per track by going to Options->Audio->System... I don't remember what it's called but its on the upper left hand corner of the Audio settings dialog, in the same area where you set the max number of tracks.
Hope this helps.
69 Shades of Red
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Attack life, it's gonna kill you anyway!