Header changes not allowed

[WB_UserParticipant]

Adjustments in header 7 and saving changes gives an error message.
As an example: When changing the logo, saves the changes and press the update button.
Error message:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at webmaster@www.md-performance.nl to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

The webmaster send me this yesterday, is there any connection?
Een fout van het type E_ERROR werd veroorzaakt op regelnummer 26 van het bestand /www/htdocs/mdperfo/site/wp-content/themes/sport/s7upf_templates/elements/mini-cart.php. Foutmelding: Uncaught Error: Call to a member function get_cart() on null in /www/htdocs/mdperfo/site/wp-content/themes/sport/s7upf_templates/elements/mini-cart.php:26
Stack trace:
#0 /www/htdocs/mdperfo/site/wp-content/themes/sport/7upframe/class/temlate.php(50): include()
#1 /www/htdocs/mdperfo/site/wp-content/themes/sport/7upframe/element/vc-minii-cart.php(34): S7upf_Template::load_view(‘elements/mini-c…’, false, Array)
#2 /www/htdocs/mdperfo/site/wp-includes/shortcodes.php(325): s7upf_vc_mini_cart(Array, ”, ‘s7upf_mini_cart’)
#3 [internal function]: do_shortcode_tag(Array)
#4 /www/htdocs/mdperfo/site/wp-includes/shortcodes.php(199): preg_replace_callback(‘/\\[(\\[?)(s7upf_…’, ‘do_shortcode_ta…’, ‘[vc_row full…’)
#5 /www/htdocs/mdperfo/site/wp-includes/class-wp-hook.php(286): do_shortcode(‘[vc_row full…’)
#6 /www/htdocs/mdperfo/site/wp-includes/plugin.php(208): WP_Hook->apply_filters(‘[vc_row full…’, Array)
#7 /www/htdocs/mdperfo/site/wp-content/plugins/wordpress-seo/admin/links/class-link-watcher

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