Hi,
The script which you tried and the facing exception will helps to solve it..
see below example:
WebDriver driver=new FirefoxDriver();
driver.get("
http://seleniumtrainer.com/components/drag-and-drop/");
driver.manage().timeouts().implicitlyWait(60, TimeUnit.SECONDS);
WebElement dragElement=driver.findElement(By.id("draggable"));
WebElement dropElement=driver.findElement(By.id("droppable"));
Actions dd=new Actions(driver);
dd.dragAndDrop(dragElement, dropElement).build().perform();
Thank You,
Murali