PHP: mkdir + thumb-problem

Code: PHP

// nächste autoincrement Nummer = ID wird bestimmt um bei den img-URLs den Ordnernamen (=ID) anzugeben
		$next_id_query = mysql_query("SHOW TABLE STATUS LIKE '$dbtable'") 
			or die ("<p>Couldn't get the next autoincrement ID, stupid situation, nm</p>");
		$next_id_row = mysql_fetch_assoc($next_id_query);
		$next_id = $next_id_row['Auto_increment'];
		$abstract_edited = str_replace('news/(ID)/', 'news/'.$next_id.'/', $abstract_edited);
		article_edited = str_replace('news/(ID)/', 'news/'.$next_id.'/', article_edited);
		
		mkdir('/'.$next_id) or die ("<p>Was too drunk to create a folder, it' s my fault I know</p>");

Code: PHP

 
function create_thumbs($file_dir, $file, $width, $height, $type, $longer_2be, $preview_quality, $save_dir)
	{
	switch ($type)
	{
		case 1:
			$image = imagecreatefromgif($file_dir."/".$file);
			header('Content-type: image/gif');
			break;
		case 2: 
			$image = imagecreatefromjpeg($file_dir."/".$file);
			header('Content-type: image/jpeg');
			break;
		case 3: 
			$image = imagecreatefrompng($file_dir."/".$file);
			header('Content-type: image/png');
			break;
		default:
		return false;
		break;	
	}
	
	if ($width < $height)
	{
		$resize_factor = (float) ($height/$longer_2be);
		$new_height = (int) $longer_2be;
		$new_width = round($width/$resize_factor);
	}
	else
	{
		$resize_factor = (float) ($width/$longer_2be);
		$new_width = (int) $longer_2be;
		$new_height = round($height/$resize_factor);
	}
	
	$preview = imagecreatetruecolor($new_width, $new_height);
	imagecopyresampled($preview, $image, 0,0,0,0, $new_width, $new_height, $width, $height);
	imagejpeg($preview, $save_dir.$file, $preview_quality);
};