After Update to Version 2.6.0 the plugin doesn’t work on Multisite

Hey Community,
when I want to switch to the individual multisites dashboard after updating to the latest version from the network administration page, this error appears everywhere (except on the first page ID=1). Does anyone have any help?

Fatal error: Uncaught Error: Call to a member function add_cap() on null in /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/classes/Facade.class.php:435 Stack trace: #0 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/classes/Facade.class.php(34): PostExpirator_Facade->set_default_capabilities() #1 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/classes/Facade.class.php(43): PostExpirator_Facade->__construct() #2 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/post-expirator.php(1643): PostExpirator_Facade::getInstance() #3 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/post-expirator.php(1646): postexpirator_launch() #4 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-settings.php(357): include_once('/homepages/33/d...') #5 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-config.php(110): require_once('/homepages/33/d...') #6 /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-load.php(50): in /homepages/XX/XXXXXXXX/htdocs/XXXXXX/jfb/wp-content/plugins/post-expirator/classes/Facade.class.php on line 435