XF 2.1 Fatal error: Uncaught InvalidArgumentException: Container key 'db' was not found

[Paridus]

I wanted to upgrade the forum to the latest version and get the following error messages:

Fatal error: Uncaught InvalidArgumentException: Container key 'db' was not found in /home/www/dps3333/html/src/XF/Container.php:43 Stack trace: #0 /home/www/dps3333/html/src/XF/App.php(931): XF\Container->offsetGet('db') #1 /home/www/dps3333/html/src/XF/Container.php(28): XF\App->XF\{closure}(Object(XF\Container)) #2 /home/www/dps3333/html/src/XF/App.php(2528): XF\Container->offsetGet('em') #3 /home/www/dps3333/html/src/XF/App.php(2591): XF\App->em() #4 /home/www/dps3333/html/src/XF.php(672): XF\App->repository('XF:User') #5 /home/www/dps3333/html/src/XF.php(452): XF::repository('XF:User') #6 /home/www/dps3333/html/src/XF/Error.php(353): XF::visitor() #7 /home/www/dps3333/html/src/XF/App.php(2200): XF\Error->displayFatalExceptionMessage(Object(InvalidArgumentException)) #8 /home/www/dps3333/html/src/XF.php(168): XF\App->displayFatalExceptionMessage(Object(InvalidArgumentException)) #9 [internal function]: XF::handleException(Object(InvalidArgumentException)) #10 {main} thrown in /home/www/dps3333/html/src/XF/Container.php on line 43