TYPO3 Core

Having the same problem here.

also present in 6.2.9

The problems seems to be located at typo3\sysext\sys_action\Classes\ActionTask.php on line 569 (JSCode-Function).
Its using the deprecated function dbFileCon() which does not return any JS for me. Replacing with printNeededJSFunctions() will fix the javascript error and show up the browser on click but the selection wont be returned to the form value.

protected function JScode() {
        $this->t3lib_TCEforms = GeneralUtility::makeInstance('TYPO3\\CMS\\Backend\\Form\\FormEngine');
        $this->t3lib_TCEforms->backPath = $GLOBALS['BACK_PATH'];
        $js = $this->t3lib_TCEforms->printNeededJSFunctions();
        //$this->taskObject->doc->JScodeArray[] = $js;
        //\TYPO3\CMS\Core\Utility\DebugUtility::debug($this->t3lib_TCEforms->printNeededJSFunctions());
        return $js;
    }

also present in 6.2.11

Just a note: Right now I'm using Extension "my_user_management" as a replacement for this core function.

Thank you for the tip. The extensions seems to be very useful but creating backend users by a model is not possible as it is with the sys action.

Unfortunately, the problem is also in 6.2.12. still not eliminated. Very very sad. Impossible.

But the patch works. Many Thanks.