Gradebook

I tried posting on this issue in the Roles forum, but no one was able to help. One poster recognised the problem, but did not know a solution.

Over the summer, I upgraded to 1.9.5+. I backed up the courses and restored them without user data. However, all the previous students still appear in the grade report for each individual assignment! Old students are NOT listed as participants, nor under "student" roles. They do NOT show up in the Grade Book. The students are not even listed in Site Administration. I tested a new blank course from scratch, and had the same problem. Even with only one student enrolled in the class, all the old students from previous years appear in the assignment grade, but not in the grade book.

Any help would be greatly appreciated....