Code:
if ($_FILES['screenshot']['error'] > 0) {
  echo 'Error: ' . $_FILES['screenshot']['error'] . '<br />';
  }else {
	$u_img = $temp.$usr.'.png';
	echo 'New Filename: ' . $u_img . '<br />';
	$img = $temp.basename($_FILES['screenshot']['name']);
	echo 'Uploaded: ' . $img . '<br />';
	
  echo "Type: " . $_FILES["screenshot"]["type"] . "<br />";
  echo "Size: " . ($_FILES["screenshot"]["size"] / 1024) . " Kb<br />";
  echo "Stored in: " . $_FILES["screenshot"]["tmp_name"] . " <br />";
	
	if( move_uploaded_file($phpbb_root_path.$_FILES['screenshot']['tmp_name'],$img )) {
   	echo 'The file '. $u_img . ' has been uploaded<br />';
		}else{
		echo "There was an error uploading the file, please try again!";
		}
	}
i think its the paths... the php temp dir is /tmp

here is the output of the code:

New Filename: generator/temp/Static.png
Uploaded: generator/temp/Wallpaper.png
Type: image/png
Size: 45.6708984375 Kb
Stored in: /tmp/phpv4PjL3
There was an error uploading the file, please try again!

the generator folder + all sub dirs are set to 777 so i know its not that...