STICK EMI is a reference to the controller sticks getting Electro-Magnetic Interference.
The RC sticks uses Hall-Effect sensors. If there's a source of magnetism near them, or parts of the controller have been magnetised, it'll show the STICK EMI error.
Move the controller away from anything else and restart it. If that doesn't resolve the issue, let us know.
At least, that's from what I understand. msinger will know better!