Unity错误——1.error CS1704: An assembly with the same name `UnityEngine.UI' has already been imported.

今天在使用Unity5.5.0时，开启昨天的Unity 工程出现如下错误：

1.error CS1704: An assembly with the same name `UnityEngine.UI' has already been imported. Consider removing one of the references or sign the assembly


2./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/GUISystem/UnityEngine.UI.dll (Location of the symbol related to previous error)


3./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/GUISystem/Standalone/UnityEngine.UI.dll (Location of the symbol related to previous error)


4.error CS1704: An assembly with the same name `UnityEngine.Networking' has already been imported. Consider removing one of the references or sign the assembly


5./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/Networking/UnityEngine.Networking.dll (Location of the symbol related to previous error)


6./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/Networking/Standalone/UnityEngine.Networking.dll (Location of the symbol related to previous error)


7.error CS1704: An assembly with the same name `UnityEngine.HoloLens' has already been imported. Consider removing one of the references or sign the assembly


8./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/UnityHoloLens/Runtime/UnityEngine.HoloLens.dll (Location of the symbol related to previous error)


9./Applications/Unity 5.5 navmesh/Unity navmesh.app/Contents/UnityExtensions/Unity/UnityHoloLens/RuntimeEditor/UnityEngine.HoloLens.dll (Location of the symbol related to previous error)


10. 

解决方法：

1. 关闭当前工程；
2. 删除工程所在目录的Library文件夹
3. 重启工程，Unity讲重新写入相关Library，即可解决问题。