This code from CodeIgniter.php

will obviously generate a “404 Page Not Found” error when the requested method is not found. In some cases you can fix this by making sure your classes have an index() method, even if it does nothing.
This is likely to be a common cause of the logging of “404 Page Not Found” errors with no page shown, which has irritated several posters here.
I haven’t posted this as a bug because it is probably what Rick intended. However it would surely be sensible to raise a different error for missing methods than for missing pages.

If I have index method in my controller and index does nothing, by ex. in Users controller with address http://example.com/users/ I make redirect in index method to default action which is login() / profile() for “not logged in / logged in” users. Case you are describing occurs when visitor(human or robot or whatever it is) rewrites url manually and in that case this error message is IMHO OK.

Whatever the reason, a “404 Page Not Found” error - with no further information - is not an acceptable way to log an error. Fixing this has saved me a significant of debugging time.

In CodeIgniter.php try changing

to

Also, In system/libraries/Router.php

line 217 and 240 (or so):

replace

with: