How can I use AutoTrader with multiple TWS accounts ?
Make as many copies of AutoTrader program as you have TWS accounts, placing each copy in its own folder. Start your TWS one at a time, say you have two TWS accounts. On the first TWS, change the API port to 7497. Then start the first copy of AutoTrader. In the AutoTrader preferences, change the port number to 7497. You may now connect this copy of AutoTrader with your first TWS account. Next start a second copy of TWS, the port value of this should be ok at 7496 (each copy of TWS running must use a unique port number). Next start the second copy of AutoTrader and connect. You can now trade each account independently using AutoTrader.
