Upgrade from 5.1.6 to 5.2.5 fails

Hello,

We are trying to upgrade our development shop from version 5.1.6 to 5.2.5 but if fails.

Our development shop is installed in /dev subfolder so we do not have issues with licenses.

We have modified config.php so it points the shop to a different database and the s_core_shops table, base_path to /dev. The development shop loads ok as well as the backend but when we try upgrading to 5.2.5 the upgrade fails with:

Fatal error : Uncaught exception ‚Enlight_Controller_Exception‘ with message ‚Controller „dev“ not found‘ in /****/****/public_html/engine/Library/Enlight/Controller/Dispatcher/Default.php:486 Stack trace: #0 /****/*****/public_html/engine/Library/Enlight/Controller/Front.php(226): Enlight_Controller_Dispatcher_Default->dispatch(Object(Enlight_Controller_Request_RequestHttp), Object(Enlight_Controller_Response_ResponseHttp)) #1 /****/****/public_html/engine/Shopware/Kernel.php(153): Enlight_Controller_Front->dispatch() #2 /****/****/public_html/vendor/symfony/http-kernel/HttpCache/HttpCache.php(492): Shopware\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #3 /****/****/public_html/engine/Shopware/Components/HttpCache/AppCache.php(255): Symfony\Component\HttpKernel\HttpCache\HttpCache->forward(Object(Symfony\Component\HttpFoundation\Request), true, NULL) #4 /****/****/public_html/vendor/symfony/http-kernel/HttpCache/HttpCache.php(449): Shopware\Components\HttpCache\AppCache->forwa in /*****/*****/public_html/engine/Library/Enlight/Controller/Dispatcher/Default.php on line 486
503 Service Unavailable

even before the upgrade begins.

Please help.

Thank you,

Nick