I'm pretty sure the problem is because of your internet connection. I've had that message quite a few times before when my router was acting up.
Downside is that you lose some time and probably get timed out, though you can have a second pilling chance. Won myself some fights having been forced to think twice instead of fast pilling, lol.
This has happened to me a few times also. A temporary fix for now is as soon as it does it to you click on the "PLAY" link on the left side of the page and rejoin the room and it'll prompt you that you have a battle going on, then just click the prompt and rejoin the battle and it should go fine from there. This is what I've done and it works every time, so do this until they fix it.