Updated MediaWiki and now get dialog "this is a test 2, do not panic" on every page

I updated our MediaWiki server from 1.13 to 1.26 and everything appears to be working OK. Except on EVERY page, a dialog pops up that says "this is a test 2, do not panic". Even if you check the box to not allow this page to create further dialogs, it appears on any page you click through. Any thoughts?