Try each of the following until the issue is resolved.

If using FAWeb version 7.83 or higher: 
  1.  Verify the marking column is editable
    1. Log into Faculty Access for the Web as Supervisor. 
    2. From the Setup menu, select Edit marking column access rights for faculty.
    3. Select the appropriate school, academic year, and session. 
    4. In the marking column grid, select Yes in the View and Edit columns for the appropriate marking columns. 
    5. Click Save. 
    6. Clear the server cache.
  2. Verify all assignments in the category have a factor greater than 0
    1. From the Gradebook menu, select Edit assignments.
    2. In the Factor column, make sure all assignments have a factor other than 0. 
    3. Click Save. 
  3. Review Number to drop settings for the category
    1. From the Gradebook menu, select Edit categories.
    2. If a number has been entered in the Number to drop column, verify this number is less than the total number of assignment grades in that category. 
      Note: If you enter a number in the Number to drop column, that number of assignment grades are allowed to be dropped, meaning the lowest assignment grade(s) will not be applied to the category average which may cause the average to be blank.  For example, if you have 10 assignment grades and your Number to drop is 11, then there will be no grades available to calculate an average from because all grades have been dropped.
  4. Refresh the gradebook to recalculate averages.

If using FAWeb version 7.82 or lower: 
  1. Verify the marking column is editable
    1. Log into Faculty Access for the Web as Supervisor.
    2. In Setup, Marking Columns, select the appropriate school, academic year, and session.
    3. In the marking column grid, select Yes in the View and Edit columns for all marking columns used in marking columns.
    4. Click Save
    5. Clear the server cache.
  2. Verify all assignments in the category have a factor greater than 0
    1. In Gradebook, select Setup, Assignments.
    2. In the Factor column, make sure all assignments have a factor other than 0.
    3. Click Save.
  3. Review Number to drop settings for the category
    1. In Gradebook, select Setup, Categories.
    2. If a number has been entered in the Number to drop column, verify this number is less than the total number of assignment grades in that category. 
      Note: If you enter a number in the Number to drop column, that number of assignment grades are allowed to be dropped, meaning the lowest assignment grade(s) will not be applied to the category average which may cause the average to be blank.  For example, if you have 10 assignment grades and your Number to drop is 11, then there will be no grades available to calculate an average from because all grades have been dropped.
  4. Refresh the gradebook to recalculate averages.