Access to wp-admin broken (Warning: Parameter 1 to wp_default_scripts() …)

Hi!

My website is down, and I can’t access the wp-admin site either..
I think the problem might be that I was using a quite old version of wp.
Can the website be recovered (and how if so?), or do I have to reinstall and build up..?

I get this messages on my website, and the same when I try to access the wp-admin site:
“Warning: Parameter 1 to wp_default_scripts() expected to be a reference, value given in /var/www/ranchequus.dk/public_html/wp-includes/plugin.php on line 571

Warning: Parameter 1 to wp_default_styles() expected to be a reference, value given in /var/www/ranchequus.dk/public_html/wp-includes/plugin.php on line 571

Warning: Cannot modify header information – headers already sent by (output started at /var/www/ranchequus.dk/public_html/wp-includes/plugin.php:571) in /var/www/ranchequus.dk/public_html/wp-includes/pluggable.php on line 1174”

Thank you so much in advance for any good advice and help!

The page I need help with: [log in to see the link]