It looks like Selenium is doing it's job and telling you when it ran into a problem, I too, cannot reach this page and get the same error. To resolve the " Error requesting http://localhost:4444/selenium-server/driver/" try running the Selenium RC server as root on that machine. Are you sure you followed all of the documentation? Is port 4444 open? Take a look at page 4 of the documentation, and make sure all of the settings are valid, including IP, port, and browser:
http://assets.nagios.com/downloads/nagi ... Nagios.pdf