My b2evolution Version: 1.9.2

Hi All,
When I have a new user in my blog and I want him to be a blogger, I insert him in the 'Bloggers' group and I give him 'Membrer' permission in the correct blog. Nevertheless the user is unable select the 'write' panel without getting the following error:

Since you're a newcomer, you'll have to wait for an admin to authorize you to post. You can also e-mail the admin to ask for a promotion. When you're promoted, just reload this page and you'll be able to blog. Smile

I have more than one user per blog and I want each one not to modify the posts of the others. What should I do?
Thanks