Note: We started on 1.6 and are now on 1.8 here, so this may not apply to 1.5.4, but....
To prevent manual enrollments (but still allow your automated database enrollments), set the "Course Enrollable" setting in each course to "No". The database field is {prefix_}course.enrollable = 0.
Enrolment
Students can enroll themselves into any class but we don't want them to
Гэтае абмеркаваньне было заблакавана, таму вы болей ня можаце адказваць на яго.