I’m connecting some gameObject A to gameObject B with a fixed joint during runtime. If there already is a Configurable Joint on gameObject B with “ProjectionMode” set to “Position and Rotation”, Unity 5.0.1 crashes every time.
I just encountered a similar issue that turned out to be a crash when attaching a joint to an inactive game object. Not sure if your issue is the same, but just in case, make sure your objects are active before setting connectedBody.
This issue is apparently fixed in 5.0.3 which must be out soon.