Coursepress errors on activation

The following error appears after activating the coursepress plugin:

Warning: implode(): Invalid arguments passed in /home/.../public_html/wp-content/themes/kleo/functions.php on line 302

I've deactivated all plugins minus coursepress and the issue continues to appear.

Here's the code from lines 301 - 303 of the functions.php file mentioned:

//custom filters
$css_target = preg_match( '/\skleo-(.*)-nav/', implode( ' ', $item->classes), $matches );
// If this isn't a KLEO menu item, we can stop here

Let me know if any additional info is needed.

tia

Note: I've confirmed that if I switch to a different theme the errors don't appear.