[TYPO3-mvc] error: Could not determine the child object type

[Thomas Mammitzsch]

hi list,

i do a custom query in my repository:

         /**
          * find user by optinCode
          * @param string $optincode
          * @return Tx_MyExt_Domain_Model_FrontendUser
          */
         public function findByOptinCode($optincode) {
		$query = $this->createQuery();
                 $query->getQuerySettings()->setRespectEnableFields(FALSE);
                 $query->matching(
                         $query->logicalAnd(
                             $query->equals('Optincode', $optincode),
                             $query->equals('deleted', 0)
                         )

                 );

                 return $query->execute();
	}

The right row is fetched from database. But when the result is mapped to 
the Tx_MyExt_Domain_Model_FrontendUser object i get a "Could not 
determine the child object type" error. Any ideas?

regards, Thomas