I've made some additional tests and I have no idea what could be wrong. I updated to forum 4.4.3 and using DNN 4.8.2, catalook installed and the main portal works just fine. If I create a forum from scratch, the general forum lets me add the post without changing settings in the main portal, I did this as well in another site (4.8.0 + catalook) and it works perfectly. But this subportal just doesn't let me add a new post. I've checked the site log and there is no error.
The only strange thing I notice is that if I pass the mouse over the "General" forum link, it says it should take me to
www.saludperfecta.com.mx/ForoGialive/tabid/186/forumid/9/scope/threads/Default.aspx
but it stays on the same page (which is http://www.saludperfecta.com.mx/ForoGialive/tabid/186/List/0/Default.aspx)
The main portal has the forum as well in http://www.colageno.com.mx/Testimonios/tabid/59/language/es-MX/Default.aspx (at the bottom of the page) and clicking on the link takes me to General forum as it should.
I'm on a dead end street right now, thanks.