Glossary Converter does not detect Multiterm

I recently upgraded to SDLTrados 2015, and when trying to convert my Excel glossaries with Glossary Converter, I get an error message: "Cannot detect Multiterm even using tbx as term base format" (translated roughly from Spanish). Never had a problem with Glossary Converter before. I uninstalled and reinstalled the latest version available, and still have the same problem. Any ideas will be greatly appreciated!