Can't get how to allow only to edit but not create new posts

Hi. The plugin looks really simple to use and this is what I’m looking for. I want to create a new rol (Proyect owner) that only allow users to edit the posts asigned to him/her but not to create new ones. I suposed that checking “Read” and “Edit published posts” capabilities will be enought. But when I logged as Proyect owner, I can’t see the “Posts” option to access to posts edition. So (as admin) I checked the “Edit posts” capability to new rol. Once again logged as Proyect owner I can see the Posts option button but I can also create new posts (and I want that this rol only could edit published posts). Do I doing something wrong? I missing something?

I’m using wordpress 3.2.1 version and everything looks working ok instead the plugin is compatible only up to 2.9.2 version.

Thanks in advance.

ps: sorry for my english

Thanks in advance