What is not correct about this statement? It came from the theme developer's files.

ERR (3): Warning: date() expects parameter 2 to be long, object given  in /home/WEBSITE/public_html/app/code/local/Peerforest/MultiProduct/Block/Product/Default/Bestseller.php on line 53

line 53 - $currentDate = date ( 'Y-m-j' , $currentDate );