Configuration System Failed to Initialize

Make sure that your config file (web.config if web, or app.config if windows) in your project starts as:

<?xml version="1.0"?>
<configuration>
    <configSections>
        <sectionGroup name="applicationSettings" 
                      type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >

            <section name="YourProjectName.Properties.Settings" 
                     type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" 
                     requirePermission="false" />

        </sectionGroup>
    </configSections>
</configuration>

Note that inside the configuration element, the first child must be the configSections element.

In the name property on section element, make sure you replace YourProjectName with your actual project’s name.

It happened to me that I created a webservice in a class library project, then I copied (overwriting) the config file (in order to bring the endpoints configuration) to my windows app and I started to have the same problem. I had inadvertently removed configSections.