Selenium: Invalid “already running” error when starting server

Question

I am trying to get the Selenium server up and running. However, when I type:

java -jar selenium-server-standalone-2.0b3.jar

I get an Exception

Answer 1

That ERROR Server Exception: sessionId should not be null; has this session been started yet? message comes from Selenium. If you're seeing it, there's a Selenium server running on that port number.