This is my error when the teacher profile opens the Admin to and view, add, admin students.
Note that in the red bullet it says 3 students and on the right it says 1 (which is a test students I just added to the course).
Side note, if it helps: I imported the course, units and everything else from another installation I had previously in another site using the Wordpress Export/Import tool.
Please make sure the buddypress items per page in the wplms->buddypress is not set to 0.
Also please make sure the theme and plugins are updated to latest versions i.e. 2.6.1