BE AJAX request delivers empty repository - typo3

Question

I want to build an BE extension that is reading the repository from another extension and delivers the data as CSV/XSL/XSLX without saving it on the server. e.g Outputs the data in a blank window with modified headers.
The BE AJAX request is fired properly with
$TYPO3_CONF_VARS['BE']['AJAX']['tx_myext::ajaxID'] = 'filename:object->method';
The repository if called from the backend does work fine too.
public function ajaxAction() {
...
$this->extRepository =& t3lib_div::makeInstance('Tx_MySecondExt_Domain_Repository_DataRepository');
...
}
but when called from domain.tld/typo3/ajax.php?ajaxID=tx_myext::ajaxID
it doesnt find Tx_MySecondExt_Domain_Repository_DataRepository also if i call the repository of the second repository with the findAll() methode directly by AJAX. It does only return NULL.
also when setting the QuerySettings by hand
public function findAllexport() {
$query = $this->createQuery();
$query->getQuerySettings()->setRespectStoragePage(FALSE);
return $query->execute();
}
Also FYI its on 4.5
Edit:
Calling the repository with the ObjectManager doesn't work too
$objectManager = t3lib_div::makeInstance('Tx_Extbase_Object_ObjectManager');
$this->extRepository = $objectManager->get('Tx_MySecondExt_Domain_Repository_DataRepository');

Answer 1

Did you make sure that the other extension is loaded before your own extension is loaded? Look at your localconf.php. Normally you need to specify the dependencies in your ext_emconf.php before you install your extension.
Also make sure that you have added both extension's configurations to the Static Includes of your TypoScript template.

Answer 2

inside the export action
... Repository to file generation
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="data.xls"');
header('Cache-Control: max-age=0');
// If you're serving to IE 9, then the following may be needed
header('Cache-Control: max-age=1');
// If you're serving to IE over SSL, then the following may be needed
header ('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); // Date in the past
header ('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT'); // always modified
header ('Cache-Control: cache, must-revalidate'); // HTTP/1.1
header ('Pragma: public'); // HTTP/1.0
... output file
exit;
done, no ajax plus pretty simple and stupid ;)
still if somone knows a awnser to the intial probelem i would appreciate it.