Why do I have negative action points? How can this happen?
If you refresh the page several times without moving, it costs an action point (because of some players refreshing repeatedly so as to be able to rob people who entered their square, without having to spend action points moving - which caused unnecessary server load). Also, asking for directions or travelling on transit cost several action points, and are possible whenever you have any action points, even if not enough.
You have to wait for these action points to be regained *past* zero before you can act again.