can't acces admin after adding a extra language. please help

[xander164]

this is the error after turning debug on:

(1/1) RuntimeException

Failed to start the session because headers have already been sent by "/var/www/vhosts/puurenstoerwonen.nl/webspace/httpdocs/puurenstoerwonen.nl/src/Adapter/EntityMapper.php" at line 99.

in NativeSessionStorage.php line 145

at NativeSessionStorage->start()in Session.php line 57

at Session->start()in SessionTokenStorage.php line 78

at SessionTokenStorage->hasToken('https-ANONYMOUS_USER')in CsrfTokenManager.php line 72

at CsrfTokenManager->getToken('ANONYMOUS_USER')in Router.php line 64

at Router->generate('admin_employees_change_form_language', array(), 0)in Link.php line 814

at LinkCore->getAdminLink('AdminEmployees', true, array(), array('action' => 'formLanguage', 'token' => '762c1510537b6d59d0ac4e3aa93a1494'))in AdminController.php line 2706

at AdminControllerCore->setMedia(false)in AdminDashboardController.php line 44

at AdminDashboardControllerCore->setMedia()in Controller.php line 291

at ControllerCore->run()in Dispatcher.php line 518

at DispatcherCore->dispatch()in index.php line 93

Edited November 14, 2023 by xander164
extra info (see edit history)