OK, I found it and have sent it to support.
My first work-around is to stop a render when the available memory dips below 1gb, save and restart the program and finish the render. Not acceptable when I have 4 such sequences to render. Are there ways to better manage the available memory?
best,
Scott
Avid MC 4.05, xp sp3, 3gb, hp xw8200 zeon