Hey, So I got a very simple test case that causes a runtime crash with WebGL (other targets run without an issue) in Unity 5 Release Candidate 1, hopefully this will help diagnose / narrow down the cause. (Case 671750) Github: https://github.com/newcommat/NodeCanvasWebGLTest or directly: https://github.com/newcommat/NodeCanvasWebGLTest.git So a brief description of the code (note this assumes understanding of the Node Canvas plugin). I have my custom class which derives from MonoBehaviour. I also have a serialised BB Variable for this class (CollectibleObject.cs) I have two actions, NullGameObject which calls BBObject.value = null; and NullCollectibleObject which calls BBCollectible.value = null; There is one gameobject in the scene with the BT, it has a blackboard variable of type UnityEngine.Object. This is then further specified (via custom Preferred Types) to be of type Collectible. If I call BBCollectible.value = null then it will crash on that provided variable, however if I just call BBObject.value = null then it will not crash (you can test this with both actions).