The permissions are set correctly I think but some users started having this problem and other users with the same usergroup and same permission, does have it.
I've tried to login with their user and password and everything works fine on my computer. The strange thing is that one of these users has tried to login from two different computer in his network and from an iPhone connected through 3G and on all three the problem comes out.
I really don't know what to do. Any suggestion?