First thing that I noticed was here:
$uploadDir = '../articles/';;
You shouldn't have two semicolons and the file destination has to be in terms of the server, so use
and put your location in from there, so if on your site the location was "/articles/" then use
$uploadDir = $_SERVER['DOCUMENT_ROOT'] . "/articles/";
Use $_FILES['userfile']['error'] to get more detailed errors rather than "Error uploading file", that might help find the problem.
I hope that solves it.