I don’t know exactly when, but after a certain time of using wordpress and a lot of manual updates to the newest version all of the sudden i was’nt able to enter the admin-interface of my WP-Multisite-Installation anymore. The last change was the installation of a modern theme.
WordPress version 4.7.x
- reinstall of WP did not solve the problem
- disabling of some plugins did not help
- database is okay
- checking or changing the apache rewrite rules did not solve the problem
Solution: adding this line to the wp-config.php helped!
define( 'CONCATENATE_SCRIPTS', false );
found the solution here: http://codex.wordpress.org