Fehler 503 bei Kunden und Bestellungen im Backend

Hallo,

ich bekomme einen Fehler ausgegeben, wenn ich im Backend auf die Menüpunkte Kunden oder Bestellungen bzw. im Menü Versandkosten klicke. Die Tabellen sind dann auch leer. In der Datenbank sind aber alle Daten vorhanden.

Hier die Fehlermeldung aus dem Log-File:

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 /homepages/24/d426386468/htdocs/shop/shopware.php(122): Shopware\Components\HttpCache\AppCache->handle(Object(Symfony\Component\HttpFoundation\Request))
#23

Kann mir jemand helfen und sagen, was da kaputt ist und wie es zu reparieren ist?

LG