One of the biggest nuisances with Android (Samsung phones especially) is sometimes the Cancel and Activate or Deactivate buttons are totally disabled or do not do anything clicking. When this happens
- Take the battery out
- Keep it shut off for a 2-3 minutes.
- Put the battery on and switch on the phone.
That is it. Now you should be able to deactivate or activate new device administrators.This fix applies when you cannot take the useless Lookout app from the Samsung phones.