Not able to to do anything on opened browser.

Hello,

Till yetserday the codes were running successfully.
Today suddenly getting exception "org.openqa.selenium.SessionNotCreatedException: session not created exception".

an someone help here to sort out the issues so that i can resume my execution.

Code:

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.ie.InternetExplorerDriver;

public class gmailtest {
public static void main(String[] args) {
//System.setProperty("java.net.preferIPv4Stack" , "true");
System.setProperty("webdriver.chrome.driver","D:\\Selenium\\chromedriver.exe");
WebDriver driver = new ChromeDriver();
driver.manage().window().maximize();
driver.manage().timeouts().implicitlyWait(20,TimeUnit.SECONDS);
driver.get("http://gmail.com");
}
}