giarosik,
Thanks for getting in touch and sorry to hear you’re having trouble here, but hopefully I can help. I’m able to successfully page between months on your site with no issues (screenshot). I’m also seeing some other Javascript errors on your site, which might be the result of a theme or plugin conflict (screenshot).
Could you try testing for conflicts and let me know what you discover? I suspect that this might be an issue related to your theme or a plugin conflict, but want to confirm before troubleshooting further.
Thanks! 🙂
-Casey-