I have now successfully found a way to have multiple units using path finding at the same time. Each of these also use a line of sight element to smooth the movement. All seems well, but when a new instance of the unit is spawned and path finding is tried with this, then the game freezes.
It can be seen in a simplified capx here
Spawn a new zombie by pressing mouse left click and each time a
black square with a red border appears, then a path has been calculated for the zombie its on.
The project folder can be seen here.
At the moment i have striped away movement of the zombies, as this seemed to work fine and only finding the path is bugging med.
Any help most appreciated.