Chrome – org.openqa.selenium.WebDriverException: unknown error: cannot get automation extension at driver.manage().window().maximize();

In general the reason you see WebDriverException: unknown error: cannot get automation extension can be numerous. The two most common cases to see this exception is :

1. Mismatch between chromedriver binary and Chrome Browser binary versions. Solution : Follow the ChromeDriver Release Notes
2. Using driver.manage().window().maximize(); to maximize the Chrome Browser. Solution : Use ChromeOptions.addArguments("start-maximized"); to maximize the Chrome Browser.

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As per your question the exception seems to be coming from one of the above cases.

Try out the following steps:

1. Kill all the chromedriver instances running in your windows Task Manager.
2. Use CCleaner tool to wipe out all the OS chores.
3. Clean all the projects in Eclipse.
4. Reboot your system once.

5. Provide the following options to start your Chrome browser:

   ChromeOptions options = new ChromeOptions();
   options.addArguments("test-type");
   options.addArguments("start-maximized");
   options.addArguments("disable-infobars");
   options.addArguments("--disable-extensions"); 
   driver = new ChromeDriver(options);
   

Your program should work with latest chrome driver 2.28 & Chrome Version 57.0.2987.110 (64-bit). Let me know if this helps you.