引发的异常：EntityFramework.dll 中的“System.Data.Entity.Core.MetadataException”

问：

我在我的 .Net 应用程序中遇到了这个问题，我最近在我的系统中克隆了这个应用程序，开始运行源代码 1.首先我得到了

编译器错误消息：并发现此 dll 不存在于 bin 文件夹中，因此从我同事的机器中复制并将其添加到我的项目 bin 文件夹中，之后我能够运行我的应用程序一次， 然后下次以后无法运行应用程序并面临以下异常 2.抛出异常：CS1069: The type name 'HttpClient' could not be found in the namespace 'System.Net.Http'

'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
Exception thrown: 'System.Data.Entity.Core.MetadataException' in EntityFramework.dll
The program '[23420] iisexpress.exe: Program Trace' has exited with code 0 (0x0).
The program '[23420] iisexpress.exe' has exited with code 2147943401 (0x800703e9).

同样在 bin 文件夹中，当我将鼠标指针放在它说忽略的文件上时，它显示如下。这会导致任何问题吗？在此处输入图像描述