If you are recieving this error message in your WP:
Oops, no such file exists! Double check the name and try again, merci.
Then your hosting provider / webserver admin has added the dir() php function to disable_functions in php.ini.
Why WP is using this insecure function is beyond me, but it seems that the developers developing WP is not that securityminded.
Feedback from WP developers to as why they are using this insecure feature would be greatly appreciated, but I suspect that no such reply from WP will be issued. This just goes to show how bad WP really is.