In Moodle 2, using SCORM 2004 the "Start a new attempt" checkbox is never available.
The problem is a variable name error in mod/scorm/locallib.php "function scorm_get_attempt_count", when the functin checks if is SCORM 1.2 or 1.3 (2004) version it check if ($scorm->version == 'scorm1_3') but the correct check is:
if($scorm->version == 'scorm_13' || $scorm->version == 'SCORM_1.3') like in loadSCO.php