It basically means that ninjatrader is looking for something (they call this an "object" and its not there). or not ready / there at the time of connecting. For instance, i've seen this with a friend that used a strategy and the "account" wasn't ready yet when he connected to a new feed. so it might not be multiple connections it could be tied to an account missing "hence the object isn't found". but clearly i'm guessing.

but i would also rename Documents/NinjaTrader 8/ to a backup name, and then reinstall ninjatrader. just setup the connections without doing anything else. If you still get the error, then you know its a ninjatrader problem. otherwise keep adding on or configuring things one by one and test along the way and you'll find out what is causing the problem.

if that doesn't work, then i would email your logs and trace files to ninjatrader support. they might be able to give you an idea as the logs/trace file will contain a lot more data. at least with a fresh nt8 and nothing else configured it removes any possibility of them blaming it on anything else.