Enable wordpress 'anyone can register' on a subdomain for coursepress pro

Hello, I have got a multisite on subdomain installation and want to create courses with coursepress pro. My first course will be a free one and anyone should be able to subscribe, in the last section I selected ‘anyone can register’, but I get a message in red, which tells me to set the wordpress blog to ANYONE can register.

I just cannot find where in the settings of that particular subdomain, to set it to ‘anyone can register’. How can I resolve this and has it something to do with ‘membership’?

Thanks, it is a great plugin