Wont let me update the database. need help.

I'm actually working on a project for school (no I'm not actually asking you do to it for me) Just trying to see what I am doing wrong...

Microsoft VB Grade Book. A teacher maintains a database containing two tables-student and grades. The students table has three fields: studentID, lastName, and firstName. The Grades table has four fields: studentID, firstExam, secondExam, and finalExam. At the beginning of the semester, the Students table is filled in completely with a record for each student in a class, and the Grades table has a record for each student that contains only the students ID number. (Note: The database is contained in the file Gradebook.accdb from the folder CH10 Databases.) Write a program that allows the instructor to record and process the grades for the semester. The program should do the following:

A) Use a navigation toolbar to fill the Grades table.

B) After all the grades have been entered, display a DataGridView control showing the name of each student and his or her semester average. The semester average should be calculated as (firstExam + secondExam + 2*finalExam) 4.

I am attaching pictures of the form that I have created (everything is binded properly i believe) For some reason it is not letting me update the database. The second one is the error I am getting. I have no idea what is going wrong. I have spent hours trying to figure it out and can't. Any help or direction is VERY appreciated.
Attachment 99709Attachment 99711

I'm not even sure if that is the problem. The first Student ID the Aj-123456 is the only one that shows up when I click through. I don't know if they are supposed to all be showing up or not when i click the next arrow in the binding navigator.