webservice 配置节点 无法识别的配置节 applicationSettings

原配置如下

  <applicationSettings>
    <Properties.Settings>
      <setting name="RelationService" serializeAs="String">
        <value>http://XXX:XXX/RelationService.svc</value>
      </setting>
    </Properties.Settings>
  </applicationSettings>

结果报无法识别配置节点，添加以下配置

  <configSections>
    <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <section name="Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5561934e089" requirePermission="false" />
    </sectionGroup>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
  </configSections>

为啥 ：https://docs.microsoft.com/zh-cn/previous-versions/dotnet/netframework-2.0/ms228114(v=vs.80) 自己看