A bug of generated C# Project on Windows Phone8.1?[Solved]

Hi everyone, I am Chinese, so my english is poor.
According to http://docs.unity3d.com/Manual/windowsstore-debugging.html, I created a C# Project, but when I open it in Visual Studio2015,then build, it show

In previous, I deleted all about Assembly-CSharp-firstpass-windows-phone-8.1 to solve it.

This problem was solved by Cannot build WSA app when "Unity C# Projects" enabled - Unity Engine - Unity Discussions

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