I get a error message when I activate "All In One SEO Pack" on

WordPress is running out of memory on your server so you’ll need to increase the memory allocated to PHP before you can activate any more plugins. Here is the WordPress documentation on how to do this – https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP

The memory-limit is set in the php settings and in the config php to 256M, but it doesn’t works. Here are the Php settings:
https://www.gleishaus.de/infophp.php

You’ll need to contact your hosting provider for help with that then. What’s happening is that you’re right around your memory limit and when you try to activate a new plugin you get an out of memory error. Typically you can just increase the memory allocated to PHP and that will fix this but if that doesn’t work then you have to contact your hosting provider for more help.