Fatal error after login

[ehrig]

Once I am logged in using the NinjaDemo shortcode (sandbox has been created successfully) I receive the following fatal error message:

Fatal error: Call to a member function get_error_code() on a non-object in /home/themetr5/public_html/admin/realty/wp-content/plugins/ninja-demo-master/classes/sandbox.php on line 589

When I reload the page, I'm logged out, and can't access the sandbox. I am using the latest NinjaDemo v1.0.13.

Can this be caused by me using it on an "admin" subdomain? If so, how to fix it without having to change to another subdomain?