I was having an issue with my remote web driver not being able to create a new remote session. It would just throw a SessionNotCreated exception.
I started off just googling for a solution like I do for most issues I run into, only to find out a lot of people get this error for a wide range of issues, I was not able to really find anything that related directly to what looked to be a solution to my issue, so that is what leads me to write this post, in hope to help anyone else that run into this issue when they get to upgrading to Selenium 3.
Long story short, the lowest version of firefox that the selenium 3 remote web driver supports is v48 so in your DesiredCapabilities you need to set your version to 48+.
DesiredCapabilities capability = DesiredCapabilities.firefox();
theBrowser = new RemoteWebDriver(new URL(“your URL”), capability);
Yeah there are a lot of other reasons you can get this exception but I only got this issue just after upgrading to Selenium 3 and if you also have this issus right after your upgrade this might help you.
Another thing that I had to add that I have not found a solution to yet is the fact that I was getting an error about firefox's plugin container when I was calling the the .quit() on the browser. I tried a few things I found online but killing the task via taskkill ended up working for now.
Runtime.getRuntime().exec("taskkill /F /IM plugin-container.exe");