Edit calendar/view.php find and change:
require_login($course, false);
TO:
if ($course == 1){
require_login($course, true);
} else {
require_login($course, false);
}
Edit calendar/view.php find and change:
require_login($course, false);
TO:
if ($course == 1){
require_login($course, true);
} else {
require_login($course, false);
}