Error Running Selenium Test with jQuery v2.0.2 and Play Framework
According to the Selenium Wiki, The HtmlUnitDriver emulates the JS behavior of (real) browsers. You may change the behavior by changing the browser it emulates. This might help as a workaround for your problem. As they state, the JS (and DOM) implementation of the HtmlUnitBrowser is not complete and bugs/problems, like the one you encountered may happen.
If possible try to work with another browser (Firefox or chrome?) and check if the Website works correctly when you open it in the browser. Open the javascript console (or Firebug if you use Firefox) and double check if your jQuery version works properly.
This bug is discussed here: https://github.com/playframework/playframework/issues/2607
It is marked closed for current versions of both Play and HtmlUnit, but so far I haven't been able to get things to work without downgrading to JQuery 1.x.