Planck's got it right... there is no way to re-enable AI after a disable AI command.
I would suggest stopping your unit some other way... try any/all of the following:
dostop
unitthen:
unit dofollow (leader
unit)
to get him moving again.
unit stop true
then:
unit stop false
Actually it may depend exactly on your situation as to what will work best. Your guy is just going to a waypoint? Maybe making a waypoint where you want him to stop, with a variable in the condition field?
Anyway, let us know how you go