I am using selenium with python and have downloaded the chromedriver for my windows computer from this site: http://chromedriver.storage.googleapis.com/index.html?path=2.15/
If you are working with robot framework RIDE. Then you can download Chromedriver.exe from its official website and keep this .exe file in C:\Python27\Scripts directory. Now mention this path as your environment variable eg. C:\Python27\Scripts\chromedriver.exe.
Restart your computer and run same test case again. You will not get this problem again.