codeigniter 404 error on live server

The most common reason for things lkike this is case sensitivity, if you develop on Windows and deploy to Linux.
You didn't say which URI caused the problem, but if your default homepage, then check that your controller is named Welcome.php and not welcome.php. Windows doesn't care, but the rest of the world does.

ps - Using "code" tags makes your post more readable

pls I have done all of that but it is still the same problem