Ideas:
-- Highly unlikely but check with ISP if you're at home. Is the port blocked? 5222, 5269, and 5298 are the defaults. If they block the ports, not much to be done short of changing providers. Public internet locations like School Campuses (including Dorms and Student Housing), Libraries, and Workplaces with BYOD all tend to block chat services like IRC, XMPP, and such, so if you're not using it at home YMMV.
-- Username is your forum name. You don't have to do the @chat.cohtitan.com anymore, it'll assume that's where you're signing into.
-- Is the error message "XMPP was unable to connect! Make sure that your XMPP login information is correct"? If it is not, what is the error message saying specifically?