From the manual


Single session only. You can not connect twice with the same user name to the TWS, the Gateway, or the IB website - not even for only checking your account. You'll get a message like "No market data during competing live session". When you log in with the TWS, the Gateway connection might break down, or vice versa. After terminating your TWS session you must therefore manually re-login from the Gateway. Zorro will automatically resume the session after an interruption, but while not connected it can not handle entries, stops, or profit targets. For working around this problem, you can register a second user for your IB account, and open the TWS with this second user name. This requires that you pay separate market data subscriptions for the second user name. The workaround does not work for IB paper accounts, which are single-user only.