Fehlermeldung bei Kundenlogin & Kundenbereich im Backend

Hallo zusammen,

vor kurzem erhielten wir in unserem Shop LovAll.de eine Fehlermeldung beim Login / Registrierung im Frontend und auch im Backend im Kundenbereich erhalten wir eine Fehlermeldung.
Im Backend im Logfile wird uns folgendes angezeigt, leider haben wir keine Ahnung wo hier der Fehler liegen könnte und sind derzeit leicht ratlos.

BadMethodCallException: Type of association must be one of *_TO_ONE or MANY_TO_MANY in /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php:1052 Stack trace:
#0 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php(1186): Doctrine\ORM\Query\SqlWalker->walkJoinAssociationDeclaration(Object(Doctrine\ORM\Query\AST\JoinAssociationDeclaration), 1, NULL)
#1 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php(842): Doctrine\ORM\Query\SqlWalker->walkJoin(Object(Doctrine\ORM\Query\AST\Join))
#2 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php(820): Doctrine\ORM\Query\SqlWalker->walkIdentificationVariableDeclaration(Object(Doctrine\ORM\Query\AST\IdentificationVariableDeclaration))
#3 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php(525): Doctrine\ORM\Query\SqlWalker->walkFromClause(Object(Doctrine\ORM\Query\AST\FromClause))
#4 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/Exec/SingleSelectExecutor.php(42): Doctrine\ORM\Query\SqlWalker->walkSelectStatement(Object(Doctrine\ORM\Query\AST\SelectStatement))
#5 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/SqlWalker.php(278): Doctrine\ORM\Query\Exec\SingleSelectExecutor->__construct(Object(Doctrine\ORM\Query\AST\SelectStatement), Object(Doctrine\ORM\Query\SqlWalker))
#6 /vendor/doctrine/orm/lib/Doctrine/ORM/Query/Parser.php(399): Doctrine\ORM\Query\SqlWalker->getExecutor(Object(Doctrine\ORM\Query\AST\SelectStatement))
#7 /vendor/doctrine/orm/lib/Doctrine/ORM/Tools/Pagination/Paginator.php(275): Doctrine\ORM\Query\Parser->parse()
#8 /vendor/doctrine/orm/lib/Doctrine/ORM/Tools/Pagination/Paginator.php(149): Doctrine\ORM\Tools\Pagination\Paginator->unbindUnusedQueryParams(Object(Doctrine\ORM\Query))
#9 /engine/Shopware/Controllers/Backend/Application.php(653): Doctrine\ORM\Tools\Pagination\Paginator->getIterator()
#10 /engine/Shopware/Controllers/Backend/CustomerQuickView.php(180): Shopware_Controllers_Backend_Application->getList(‚0‘, ‚20‘, Array, Array, Array)
#11 /engine/Shopware/Controllers/Backend/Application.php(202): Shopware_Controllers_Backend_CustomerQuickView->getList(‚0‘, ‚20‘, Array, Array, Array)
#12 /engine/Shopware/Controllers/Backend/CustomerQuickView.php(78): Shopware_Controllers_Backend_Application->listAction()
#13 /engine/Library/Enlight/Controller/Action.php(192): Shopware_Controllers_Backend_CustomerQuickView->listAction()
#14 /engine/Library/Enlight/Controller/Dispatcher/Default.php(478): Enlight_Controller_Action->dispatch(‚listAction‘)
#15 /engine/Library/Enlight/Controller/Front.php(228): Enlight_Controller_Dispatcher_Default->dispatch(Object(Enlight_Controller_Request_RequestHttp), Object(Enlight_Controller_Response_ResponseHttp))
#16 /engine/Shopware/Kernel.php(188): Enlight_Controller_Front->dispatch()
#17 /vendor/symfony/http-kernel/HttpCache/SubRequestHandler.php(102): Shopware\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#18 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(453): Symfony\Component\HttpKernel\HttpCache\SubRequestHandler::handle(Object(Shopware\Kernel), Object(Symfony\Component\HttpFoundation\Request), 1, true)
#19 /engine/Shopware/Components/HttpCache/AppCache.php(261): Symfony\Component\HttpKernel\HttpCache\HttpCache->forward(Object(Symfony\Component\HttpFoundation\Request), true, NULL)
#20 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(238): Shopware\Components\HttpCache\AppCache->forward(Object(Symfony\Component\HttpFoundation\Request), true)
#21 /engine/Shopware/Components/HttpCache/AppCache.php(102): Symfony\Component\HttpKernel\HttpCache\HttpCache->pass(Object(Symfony\Component\HttpFoundation\Request), true)
#22 /home/lovsdajq/www.lovall.de/shopware.php(122): Shopware\Components\HttpCache\AppCache->handle(Object(Symfony\Component\HttpFoundation\Request))
#23

Woran kann das liegen und wie kann dies schnellstmöglich behoben werden?

Vielen Dank
LG Jasmin