If the formula in a calculated grade is bad/wrong, it breaks other parts of the Gradebook.

Symptoms:

• Gradebook > Grader report: Grade item column containing the bad formula contains the word "Error". Student names appear as normal. "Grades for..." Link next to student name work as expected.
• Gradebook > User report: "Select all or one user" drop-down menu is empty and displays "All users (0)"; should display list of students. Grade item with bad formula contains the word "Error".
• Gradebook > Export does not work. No content is exported, just headings.

Steps to reproduce:

• course homepage: Create two Assignments
• In Gradebook > Simple view, edit the calculation for the Course total
• Add id numbers to the two assignments. e.g. 'one' and 'two'
• Add a formula to the Calculation. e.g. =sum([[one]],[[two]]). Save.
• Return to the homepage of the course and delete one of the assignments.
• Go to Gradebook > Simple view again and open the calculation for the Course total. Forumula will look something like this =sum(##gi1767##,[[two]])

See also forum thread: https://moodle.org/mod/forum/discuss.php?d=157369 Apparently this bug has made the transition from Moodle 1.9 to 2+