The absolute easiest thing you can do is use mkdir from PHP. That automatically assigns proper ownership. Otherwise, you may need to login through your webhost and chmod the directory manually using SSH.
If you are getting a white page, that indicates a fatal error, assuming that there is supposed to be some kind of output. Enable your error reporting by putting this at the top of the page:
If the only thing that has changed was the addition of error_get_last, then the error will be a non-existent function. Error_get_last is only post 5.2. To get around that, you would instead track errors with:
ini_set('track_errors', 1); // Somewhere usually at the top
echo $php_errormsg; // After your attempt to move the uploaded file
Chances are your error reporting is too low. As soon as you open it up to E_ALL, then you will likely see the error without needing to use error_get_last or $php_errormsg.