I use SoapUI Pro 5.1.2 on Win7 x32, and try to connect to Selenium Webdriver in Groovy TestStep.
For this purpose I added selenium-standalone-server.jar
This could be a compatibility issue between the 'selenium', 'chrome browser version' and 'chrome driver' version that you are using.
It you are using Selenium 2.53 (like me), then using chrome driver 2.25 should work for you.
You can download it from here - https://chromedriver.storage.googleapis.com/index.html?path=2.25/