Just updated to Astar 3.5.1, and now my game wont run because of several occurences of the same error in RVOKDTree.cs : The type or namespace name “Agent”’ could not be found.
Please help ! 
That indeed did the trick, thank you !
Hi
Unitypackages are really bad at handling updates. The RVOKDTree should not be included anymore. Try to delete the AstarPathfindingProject folder and reimport.