IIS部署.NET4.7+ C# REST API报解析实体名称错误（第5行第51位）

IIS - 网站 - 浏览 - 解析错误：解析实体名称时出错，行5位置51。

• 基于.NET 4.7+开发C# REST API；
• API通过Visual Studio完成发布；
• API以IIS服务形式安装部署；
• API作为Swagger服务运行，可通过Postman调用调试；
• 已在多台Windows Server 2016设备上测试运行正常；
• 某台安装相同.NET版本的Windows Server 2016设备上无法运行，持续抛出上述错误。

• 删除原疑似有问题的web.config段落（该段落在其他设备上运行正常），仍会报相同的实体名称解析错误，位置仍为第5行第51位；调整web.config对应行内容后，问题依旧复现；
• 尝试删除web.config中部分实体；
• 尝试重装IIS；
• 尝试查看事件查看器日志及IIS日志，均未定位到问题原因。

<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<sectionGroup name="common">
<section name="logging" 
type="Common.Logging.ConfigurationSectionHandler, Common.Logging" />
</sectionGroup>
<section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog" />
</configSections>
<appSettings file="..\..\AppSecrets.config">
<add key="cors" value="localhost;localhost2; ;" />
<add key="connection" value="web" />
<add key="waitandretry" value="3" />
<add key="circuitbreaker" value="3" />
<add key="circuitbreakertime" value="5" />
<add key="apikey" value="xxxxxx" />
</appSettings>
<common>
<logging>
<factoryAdapter type="Common.Logging.NLog.NLogLoggerFactoryAdapter, 
Common.Logging.NLog4411">
<arg key="configType" value="INLINE" />
</factoryAdapter>
</logging>
</common>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
internalLogFile="C:\inetpub\wwwroot\sms\MyAPI\logs\InnerLog.txt" 
internalLogLevel="Error" autoReload="true">
<extensions>
<add assembly="NLog.WindowsEventLog" />
</extensions>
<targets>
<target xsi:type="File" name="log" 
fileName="${basedir}\logs\${date:format=yyyy-MM-dd}.log" 
layout="${longdate} ${uppercase:${level}} ${message}" />
<target xsi:type="EventLog" name="eventlog" source="testlogging" 
log="Application" 
layout="${message}${newline}${exception:format=ToString}" />
</targets>
<rules>
<logger name="*" minlevel="Error" writeTo="log" />
<logger name="*" minLevel="Error" writeTo="eventlog" />
</rules>
</nlog>
<system.web>
<trace enabled="true" />
<compilation targetFramework="4.7.2" />
<httpRuntime targetFramework="4.6.1" />
</system.web>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.Helpers" 
publicKeyToken="xxxxxx" />
<bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" 
publicKeyToken="xxxxxx" />
<bindingRedirect oldVersion="1.0.0.0-5.2.3.0" newVersion="5.2.3.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.WebPages" 
publicKeyToken="xxxxx" />
<bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Newtonsoft.Json" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-11.0.0.0" newVersion="11.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Microsoft.Owin" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Cors" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />  
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Http" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Net.Http.Formatting" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Http.Owin" 
publicKeyToken="xxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.2.6.0" newVersion="5.2.6.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Autofac" publicKeyToken="xxxxxx" 
culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.8.1.0" newVersion="4.8.1.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Autofac.Integration.WebApi" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.2.0.0" newVersion="4.2.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Autofac.Integration.Owin" 
publicKeyToken="xxxxx" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.2.0.0" newVersion="4.2.0.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
<system.codedom>
<compilers>
<compiler language="c#;cs;csharp" extension=".cs" 
type="
Microsoft.CodeDom.Providers.DotNetCompilerPlatform. 
CSharpCodeProvider, 
Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, 
Culture=neutral, PublicKeyToken=xxxxx" warningLevel="4" 
compilerOptions="/langversion:default /nowarn:1659;1699;1701" />
<compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" 
type= 
"Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, 
Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, 
Culture=neutral, PublicKeyToken=xxxx" warningLevel="4" 
compilerOptions="/langversion:default /nowarn:41008 
/define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />
</compilers>
</system.codedom>
<system.webServer>
<handlers>
<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
<remove name="OPTIONSVerbHandler" />
<remove name="TRACEVerbHandler" />
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" 
type="System.Web.Handlers.TransferRequestHandler" 
preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>
<defaultDocument>
<files>
<add value="/swagger" />
</files>
</defaultDocument>
</system.webServer>
</configuration>

该报错本质是XML解析失败，修改web.config后仍报相同位置错误，说明IIS解析的配置文件不是你修改的目标文件，或是存在其他层级的配置文件出错，按以下优先级排查即可：

1. 先确认IIS站点配置的物理路径是否正确，确保你修改的web.config和站点指向路径下的文件为同一个
2. 排查站点引用的外部配置文件..\..\AppSecrets.config，该文件内容会被合并到web.config解析流程中，检查该文件第5行是否存在未转义的&、<等XML非法字符，或是实体名称定义错误
3. 检查父级目录的配置文件，包括站点上层目录的web.config、.NET Framework全局配置文件C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config和machine.config，排查这些文件第5行是否存在语法错误
4. 确认IIS站点应用程序池的.NET CLR版本配置为v4.0，避免低版本CLR解析高版本配置文件触发异常

内容的提问来源于stack exchange，提问作者Franco