A couple things to keep in mind:
1. Please make sure you are hitting Submit and not save as draft.
2. Please make sure you are not entering anything for withdrawn students. It will give you a message stating that persons grade has already been submitted. If you clear out the grade, it will go through for everyone else.
3. If you have submitted them correctly, you will get a message stating they have been submitted, and when you go back in, it will tell you that you cant change them because they have been submitted already