If you are using a phase coupler/amplifier in your system, some will "loop," causing constant data to be duplicated (also called a data storm). The problem prevents all other commands from being sent over the line (seems to lock up) and the AHP will have no affect (although you should see the commands running in the Activity Monitor). The only cure is to change the coupler
or, if possible, change the characteristics of the coupler you're using. Suggested models have been discussed elsewhere.