PHP warning

Illegal string offset 'uid'

/var/www/html/application/controllers/admin/surveyadmin.php(1556)

1544 /
1545 @param integer $iSurveyID
1546 /
1547 private function _getGeneralTemplateData($iSurveyID)
1548 {
1549 $aData = [];
1550 $aData['surveyid'] = $iSurveyID;
1551
1552 // Get users, but we only need id and name (NOT password etc)
1553 $users = getUserList();
1554 $aData['users'] = array();
1555 foreach ($users as $user) {
1556 $aData['users'][$user['uid']] = $user['user'].($user['full_name'] ? ' - '.$user['full_name'] : '');
1557 }
1558 // Sort users by name
1559 asort($aData['users']);
1560 $aData['aSurveyGroupList'] = SurveysGroups::getSurveyGroupsList();
1561 return $aData;
1562 }
1563
1564 /
1565 @param Survey $survey
1566 @return array
1567 */
1568 private function _getTextEditData($survey)