So, how are you supposed to erase minds with an alien?

There is a cool down phase after they use an alien power, so maybe you tried it too soon again.

*edit to add.. I just went in game to try it and wiped a coworkers memory.. my alien sim is level 9 mischief and there is nothing showing up for him to use alien powers again right away. I'm not sure how long the cool down phase is because I don't use them daily. I'll try to keep an eye on it.