Is this AccuTrack version 11.0.6? I tested here and it worked fine with that version and a tutoring sample database. If it is an older version let me know and I will get you the latest files. If not, then it may be that it is having a hard time handling the delete for all of the associated records for the students from quite a few other tables the students table is joined to. You still have a few options, though.
Option 1: You can just backup the database and use it as an archive if people want to point to it to run reports from the past. After that, you can go to (expanded view) Database >> Delete and remove the students, tutors, activities, or whatever. That will remove the records you want, but keep your configuration intact. Of course, you would only do this if you have import files ready to go.
Option 2: If you plan to import students, you can set the ones to inactive that are not on the import file. That way the students would still be in there, but set to inactive. So you could run reports on them, but they would not be able to sign in to AccuTrack. Also, If you are using a registration import, you can overwrite any existing registrations with just the ones on the import file.