Notice (8): Undefined index: EnrolleeCoPerson [APP/Model/CoPetition.php, line 405]
Warning (2): array_keys() expects parameter 1 to be array, null given [APP/Model/AppModel.php, line 103]
Warning (2): Invalid argument supplied for foreach() [APP/Model/AppModel.php, line 103]
Notice (8): Undefined index: EnrolleeCoPerson [APP/Model/CoPetition.php, line 1344]
Warning (2): array_keys() expects parameter 1 to be array, null given [APP/Model/AppModel.php, line 123]
Warning (2): Invalid argument supplied for foreach() [APP/Model/AppModel.php, line 123]

Line 405:
$coData['EnrolleeCoPerson'] = $this->EnrolleeCoPerson->filterModelAttributes($requestData['EnrolleeCoPerson']);

There's probably some missing (undocumented) attribute that needs to be set.