网上查到的 记录一下
unity2018项目，用2017版本打开就会出现预制体无法拖入视图并且报错：
Unable to instantiate prefab. Prefab may be broken.
UnityEditorInternal.InternalEditorUtility:HierarchyWindowDrag(HierarchyProperty, Boolean, HierarchyDropMode)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
解决方案：用记事本打开对应的预制体并做出以下修改：
1.将“m_SourcePrefab”改为“m_ParentPrefab”
2.将“m_IsPrefabAsset”改为“m_IsPrefabParent”