Error 4 is a Connection Timeout error. Typically your mobile provider is banned from WhatsApp (or your whole country is banned). Try from a terminal a ping to v.whatsapp.net or sro.whatsapp.net, if it doesn't reply then you can't reach the WhatsApp servers from your phone. If it does reply then I don't know what can be wrong, maybe registration is down at the moment or something. EDIT: What do you mean with RE-register your number? WhatsApp bans for that.