NetSparkle: Buttons not showing in the update window

I have installed the library in my C# project through NuGet, but every time there is an update the buttons to start downloading, to skip, or to remind the user to download later do not show up in the window, making the library impossible to use.

Here is an example of my code:

var sparkle = new Sparkle(
                Misc.Util.getUrl() + "/core/windows/agent/appcast.xml",
                Properties.Resources.Befective,
                NetSparkle.Enums.SecurityMode.Unsafe
            );
sparkle.StartLoop(true,true);