Fatal error: Call to undefined function gradebookapi_calc_grades_all_users() in /path/to/drupal/modules/gradebook/gradebook.module on line 712

I get this error after...
1) installing module (with no other contributed modules installed)
2) creating 1 gradebook
3) creating 2 categories
4) renaming the first category (error occurs after saving changes)

Environment
PHP version: 5.2.1
MySQL version: 4.1.22-standard
Apache version: 1.3.37 (Unix)
Drupal 5.1

Let me know if you need to know anything else.