CafeTran Espresso can connect to some independent online MT services (e.g. MyMemory, Google Translate, DeepL) via their APIs or web browser interfaces. They may stop working for various reasons. For example, they may have an issue with their online MT server or the website may take some maintenance break. After a while, it can start working again.

The given website or MT service can also update  user interface to the new version. If this is the case, CafeTran needs to be updated as well to adjust to the change if the MT service provider still makes it possible. The best solution in such cases is to switch to another MT service or use the ones available via the web interface as described here.