General help

I've yet to upload any files successfully in Moodle. Here is the error message I've been receiving:

"An unknown problem occurred while uploading the file 'castle.jpg' (perhaps it was too large?)"

I'm using Moodle on a Mac laptop, and here are my config.php data:

$CFG->wwwroot = 'http://localhost/moodle';
$CFG->dirroot = '/Library/WebServer/Documents/moodle';
$CFG->dataroot = '/Library/WebServer/moodledata';
$CFG->directorypermissions = 0777;

Thanks,
Randall