Error: Configuration system failed to initialize

I'm developing an application in C# and during development I came across the following error:

Inthefile:Settings.settingsthereisastringthatstorestheusername.Apparentlythismaybetheproblem,butIneedthisstring.Whatisthesolution?

Code:

namespaceMarcaBus.Properties{[global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()][global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "11.0.0.0")]
internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase {

    private static Settings defaultInstance = ((Settings)(global::System.Configuration.ApplicationSettingsBase.Synchronized(new Settings())));

    public static Settings Default {
        get {
            return defaultInstance;
        }
    }

    [global::System.Configuration.UserScopedSettingAttribute()]
    [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
    [global::System.Configuration.DefaultSettingValueAttribute("")]
    public string Usuario {
        get {
            return ((string)(this["Usuario"]));
        }
        set {
            this["Usuario"] = value;
        }
    }
}

}

In the file app.config I added a line to force execution with level Administrator:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <requestedExecutionLevel level="requireAdministrator" uiAccess="false" />
    <configSections>
        <sectionGroup name="userSettings" type="System.Configuration.UserSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
            <section name="MarcaBus.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" allowExeDefinition="MachineToLocalUser" requirePermission="false" />
        </sectionGroup>
    </configSections>
    <userSettings>
        <MarcaBus.Properties.Settings>
            <setting name="Usuario" serializeAs="String">
                <value />
            </setting>
        </MarcaBus.Properties.Settings>
    </userSettings>
</configuration>