Problme to add who be able to read and moderate the forum

First of all, sorry if i post in the wrong way but i cant post anywhere, i dont know why.

The problem was the follow:

I am trying add who will be able to read and moderate the forum but it appears be impossible. i wnet in the acp in the content(forum view), click in the category and try add, but all the time I click in Add, nothing appear.

My question was: What was happens? Are there any other place that i can do it?

Thanks.

Paulo Paiva
CEO of Valor Brasileiro.