If you have started to grade directly in the question's rubric within the questions list, you've disabled the option for grading with the grade buttons.

TomaGrade offers two grading methods:

1. Grade Buttons: The toolbar 'G' button (and the minus and plus annotations), and the 'mini G' beside each question of the questions list:


2. Direct Typing: Input grades directly into the question list (the grade array).

You cannot use both methods at the same time, thus when you try to type directly into the array for the first time, you get the following message:

By clicking OK in this window, you will only be able (for this specific exam notebook) to give grades directly in the array.

If you wish to re-enable the option for grading with the grading buttons you can reset the notebook's grading. 

Note that resetting the exam notebook will reset any grades and comments given to the notebook.

You'll be able to read more about reset options here.