Crash during Script Call Optimization

Hello, Our application is crashing only when the 'Script Call Optimization' is set to 'fast but no exception'. Here is the call stack. What confuses me is the UpdateRetargetIKWrite, no where in the app we use IK, nor avatars. Has anybody dealt with this issue UnityEngine::Animation::SetBoundCurveFloatValue(...) #17 UnityEngine::Animation::SetGenericFloatPropertyValues(...) Animator::UpdateAvatars(...) AnimatorManager::UpdateRetargetIKWrite() PlayerLoop(bool, bool, IHookEvent*) UnityPlayerLoop UnityRepaintImpl(bool) __51-[UnityAppController(...) thanks in advance cheers matt