In my recent experience, when you are using multiple accounts to invite friends to an event, you are bound to get the narrow list error sooner than later.
The best thing I can suggest is to space the invite batches out over a certain period of time and randomize the number of friends per batch (30-50 should be fine).
Still, you very well might get the narrow list error. It really sucks, especially when you have accounts that are maxed out at 5,000 friends.
Post back with your results if you do not mind.
Thanks and good luck!