Drupal custom page with wildcards in url not working
By using the named wildcards %id and %name as wildcards, Drupal will look for functions named id_load() and name_load(). It will pass the values of these wildcards to those functions, and use the return values as the arguments passed to the page callback. If the _load functions are not found, or if a FALSE value is returned, or no value is returned, you will get the error you are seeing.

I'm suspecting you want your path to be:

course-details/%/%