Error [500]

Class "JResponse" not found
.../plugins/system/regacymailing/regacymailing.php:705
700 			}
701 			$stylestring .= '</style>'."\n";
702 		}else{
703 			$stylestring = '<style type="text/css">'."\n".$style."\n".'</style>'."\n";
704 		}
705 		$body = JResponse::getBody();
706 		$body = preg_replace('#</head>#', $stylestring.'</head>', $body, 1);
707 		JResponse::setBody($body);
708 	}
709 
710 	function onUserBeforeSave($user, $isnew, $new){