Actually, I figured out what's causing it... maybe I'm using it wrong. I have one main FSM and a disabled FSM that is on another game object, which is a child of the main object (where the main FSM is). This main FSM, when it enters the idle state, enables the child fms (patrol). That state (where it enables the patrol fsm) then checks every few frames (I have a custom action that does this) to see if it detects a target, at which point it leaves the state and sets the target (this all works fine). The issue is that if I leave "Reset On Exit" checked for the Enable FSM action, it causes it to lock up on the first SendMessage action in the next state. Oddly, if the first action in the next state is a GetComponent action, that one triggers, but the SendMessage actions still freeze.
Anyway, sending a repro project is going to be tricky, but if necessary I can try to figure it out. Before I do though, I wanted to make sure it wasn't obvious based on that extra info (either what the problem is, or what I'm doing wrong). Thanks.
More Info:
I actually found I can leave Reset on Exit on if I move that action to the bottom of the action list. Not sure if its being the last action, or if its being after my custom action that causes it to start working, but that's what is happening.