关于 Visual Studio：在 VS 2015 社区版中将 .Net 框架从 4.5.2 更改为 4.5 时出现编译错误

Compilation Error when change .Net framework from 4.5.2 to 4.5 in VS 2015 Community edition

在 VS 2015 社区版中将我的 .Net 框架从 4.5.2 更改为 4.5 之后。我收到以下错误。有谁知道问题是什么以及如何解决这个问题。看起来编译版本不同，但我已经将我的 web.config 修改为 4.5

Server Error in '/' Application.

Compilation Error Description: An error occurred during the
compilation of a resource required to service this request. Please
review the following specific error details and modify your source
code appropriately.

Compiler Error Message: CS1617: Invalid option '6' for /langversion;
must be ISO-1, ISO-2, 3, 4, 5 or Default

Source Error:

[No relevant source lines]

Source File: Line: 0

Show Detailed Compiler Output:

C:\\Program Files (x86)\\IIS Express>
"C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319\\csc.exe" /t:library
/utf8output /R:"C:\\Users\\admin\\AppData\\Local\\Temp\\Temporary ASP.NET
Files\
oot\\479d40ee\\add72695\\assembly\\dl3\\31bb6ea7\\6a8168a8_dae8d001\\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.dll"
/R:"C:\\WINDOWS\\Microsoft.Net\\assembly\\GAC_MSIL\\System.Configuration\\v4.0_4.0.0.0__b03f5f7f11d50a3a\\System.Configuration.dll"
/R:"C:\\WINDOWS...................

Microsoft (R) Visual C# Compiler version 4.6.0079.0

for C# 5 Copyright (C) Microsoft Corporation. All rights reserved.

This compiler is provided as part of the Microsoft (R) .NET Framework,
but only supports language versions up to C# 5, which is no longer the
latest version. For compilers that support newer versions of the C#
programming language, see
http://go.microsoft.com/fwlink/?LinkID=533240

error CS1617: Invalid option '6' for /langversion; must be ISO-1,
ISO-2, 3, 4, 5 or Default