Coursepress errors: array_key_exists(): etc..

Hi,

I've just set up Coursepress on my localhost site, and I'm just trying to preview the test course that comes with the plugin, but I get a bunch of errors when clicking on any of the course units:

Warning: array_key_exists(): The first argument should be either a string or an integer in /Applications/XAMPP/xamppfiles/htdocs/uncoveryourblueprint/wp-includes/cache.php on line 680

Warning: Creating default object from empty value in /Applications/XAMPP/xamppfiles/htdocs/uncoveryourblueprint/wp-content/plugins/coursepress/includes/classes/class.shortcodes.php on line 3337

Warning: array_key_exists(): The first argument should be either a string or an integer in /Applications/XAMPP/xamppfiles/htdocs/uncoveryourblueprint/wp-includes/cache.php on line 680

I saw you answered a similar question, saying it was just a PHP error - nothing to worry about, and to make sure debug was turned off. Mine is off..

I dont think I've even got around to modifying anything yet.
Can you help?

Thanks.