Blog posting permission from stream

Hi

I am sure this is just a setting but I can't find it anywhere!

I have a user type who is not allowed to make blog posts. From EB they cannot post, there is no create post icon/option. But from the stream they do have the create blog option. It actually won't let them post, and an error appears but doesn't say anything. Where can I turn of the blog posting option from the stream by user type? And where can I set the error messages?

Thanks