When I go into Individual Grades Entry to either enter or edit a Student's alpha or numeric score, I cannot edit it, despite the fact I have security rights to do so.
The most common reason is you are outside the grades-entry period. Go here: Setup > Preferences > Grades. Under Grades Entry Form at lower left, note the days before and days after settings. You must either be entering within that window or expand that window to include the day(s) you want to work. Note: These settings control SchoolLogic and TeacherLogic operators. They do not control SIRS or StudentsAchieve operators.