I solved this error by installing the browser driver:
- Navigate your browser to seleniumhq.org website
- Select the Downloads tab
- Scroll down the page to the Browser section and download the driver you want by clicking the link, for example, Google Chrome Driver
- Double-click the downloaded file, for example, chromedriver_mac64(1).zip
- Double-click the extracted file, for example, chromedriver
Reference: search YouTube.com for the error
Platform: macOS High Sierra 10.13.3