[]layaair3D导出场景错误TypeLoadException

在unity中使用LayaAir3D插件导出场景的时候一直报这个错误TypeLoadException: Could not load type 'UnityEngine.ImageConversion' from assembly 'LayaAirLibrary'.
LayaExport.DataManager.getSceneNode ()
LayaExport.DataManager.saveData ()
LayaExport.DataManager.getData ()
LayaAir3D.exportResource (Boolean isDebug) (at Assets/LayaAir3D/LayaTool/LayaAir3D.cs:435)
LayaAir3D.OnGUI () (at Assets/LayaAir3D/LayaTool/LayaAir3D.cs:337)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
那个大大知道这是怎么回事，，layaair3D插件版本是1.7.16、unity版本5.6.5f1