Hi Diego,
It sounds like you did not use the Web.config file that shipped with mojoPortal and you are missing a tag declaration in your Web.config file as well as some other settings related to the editors and jquery are probably not correct. You should use the Web.config that shipped with mojoPortal and restore any customizations such as machine key from your old one.
Note that you no longer have to maintain the <system.net.mail section because it is no longer used. Only the settings in user.config are used for email now.
Hope that helps,
Joe