It works fine now. Thank you!!

This is the link to the post at jetpack support where I am trying to get help from them.

I have found the incompatibility. The problem is related to the modules "Social", "Sharing" and "contact form" (at least I think so).

It's a conflict with JetPack plugin. I wouldn't like to deactivate JetPack. How can I proceed?

@dimalifragis No idea how to do it.

Solved. Unistall and instal again.

@dimalifragis When I click on forum tab I get this: But when I click on a subforum I get this: I have deactivated all the plugins...

@robert No, I don't. I have the page hosted in a managed wordpress service (godaddy) so I am not sure about it they are caching something.