When you did the security update, you changed to the 10.11.6 (15G1212) version. This makes the previous WebDriver-346.03.15f04 obsolete, luckily a new web driver is available (346.03.15f05). Install it and you are back in business. ADVICE: keep a copy of all revisions of the web drivers for you Mac OS version. WebDriver-346.03.15b01 will also work after the security update, and in my case also automatically updated to the new 346.03.15f05 version. KAB.