Technical Issue with AIOS

Hello,

I am receiving error message caused by AIOS. I am running this plugin on multiple websites with same themes, only this one is causing an error:

Fehler-Details
==============
Ein Fehler vom Typ E_ERROR wurde in der Zeile 739 der Datei XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/classes/wp-security-user-login.php verursacht. Fehlermeldung: Uncaught Error: Call to undefined function wp_strip_tags() in XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/classes/wp-security-user-login.php:739
Stack trace:
#0 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-includes/class-wp-hook.php(324): AIOWPSecurity_User_Login->aiowps_login_message('')
#1 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-includes/plugin.php(205): WP_Hook->apply_filters('', Array)
#2 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/other-includes/wp-security-rename-login-feature.php(219): apply_filters('login_message', '')
#3 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/other-includes/wp-security-rename-login-feature.php(1366): login_header('Anmelden', '', Object(WP_Error))
#4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/classes/wp-security-process-renamed-login-page.php(217): require_once('/www/htdocs/w01...')
#5 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/classes/wp-security-wp-loaded-tasks.php(21): AIOWPSecurity_Process_Renamed_Login_Page::renamed_login_init_tasks()
#6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-content/plugins/all-in-one-wp-security-and-firewall/wp-security-core.php(493): AIOWPSecurity_WP_Loaded_Tasks->__construct()
#7 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-includes/class-wp-hook.php(324): AIO_WP_Security->aiowps_wp_loaded_handler('')
#8 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#9 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#10 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-settings.php(726): do_action('wp_loaded')
#11 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-config.php(104): require_once('/www/htdocs/w01...')
#12 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-load.php(50): require_once('/www/htdocs/w01...')
#13 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/wp-blog-header.php(13): require_once('/www/htdocs/w01...')
#14 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/index.php(17): require('/www/htdocs/w01...')
#15 {main}
  thrown

How can I solve this issue?

BR
Patrick