System.Configuration.SettingsPropertyNotFoundException: when attempting to access SSRS report execution service

Question

I have a .Net 4.0 project that has a web reference to the Report Execution Service. When I run my test code against this it works fine. However when I migrate to another machine calls to the service fail with:

System.Configuration.SettingsPropertyNotFoundException: The settings property 'MyNamespace_localhost_ReportExecutionService' was not found.

My Settings.settings file looks like this:

    [global::System.Configuration.ApplicationScopedSettingAttribute()]
    [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
    [global::System.Configuration.SpecialSettingAttribute(global::System.Configuration.SpecialSetting.WebServiceUrl)]
    [global::System.Configuration.DefaultSettingValueAttribute("http://localhost:8080/ReportServer/ReportExecution2005.asmx")]
    public string MyNamespace_localhost_ReportExecutionService {
        get {
            return ((string)(this["MyNamespace_localhost_ReportExecutionService"]));
        }
    }

The app.config looks like this:

<applicationSettings>
    <MyNamespace.Properties.Settings>
        <setting name="MyNamespace_localhost_ReportExecutionService"
            serializeAs="String">
            <value>http://localhost:8080/ReportServer/ReportExecution2005.asmx</value>
        </setting>
    </MyNamespace.Properties.Settings>
</applicationSettings>

As far as I can tell, this is correct. I have tried dropping and recreating the web service reference with no effect. I am out of ideas at this point. Again, this works on my dev machine. The issue occurs when I put this assembly on another server. The execution service is running on that server as I can get to it through the url.

Does anyone know what the issue might be?