Log in/Human Captcha error: “Illegal string offset ‘obr_hlc’

Hi all,

Went to log in and edit this website and found the human captcha was replaced with the following:

Warning: Illegal string offset ‘obr_hlc’in /var/sites/e/edinburghtransplant.org/public_html/wp-content/plugins/humancaptcha/outerbridge-humancaptcha.php on line 219

Warning: Illegal string offset ‘obr_hlc’ in /var/sites/e/edinburghtransplant.org/public_html/wp-content/plugins/humancaptcha/outerbridge-humancaptcha.php on line 220

I’ve had a look through the wordpress folders to find the relevant php file but can’t seem to locate it.

Has anyone else come across this problem? And has anyone resolved it and prevented it from happening in the future?

Thank you!

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