Show custom post type by custom taxonomy

Hi,
I can't list a cpt for it's own custom taxonomy.

I created a cpt (professor) and a custom taxonomy (class) for this cpt with the CPT UI plugin.
To show these cpt I created an archive page by copying the archive.php page and renaming it to archive-professor.php
So far I can see all the professor cpt. :)
So in secondary navigation I created a menu for this custom taxonomy with 4 categories. When I try to list the posts with any of the categories it returns page not found.

Did I miss something here?

I just want to list the posts , all or by category.