Looking at it in Firebug, there's an error in line 9 of jquery.plus1.js:
jQuery('.' + Drupal.settings.plus1.widget_class, context).each(function () {
The error is given as "Drupal.settings.plus1 is undefined".
I would suggest posting in the Issue queue for that module.
Date: Tue, 9 Aug 2011 15:01:55 +0100 From: Chris G cl@isbd.net Subject: [support] Why would an upgrade to the Plus_1 module mess up some (javascript?) pull-down menus? To: support@drupal.org Message-ID: 20110809140155.GA5646@chris Content-Type: text/plain; charset=us-ascii
I have been slowly working my way to finding which module update had caused this problem, finally found it today, updating the Plus_1 module from version 6.x-2.6 to version 6.x-2.7 breaks the pull down menus on this site.
The working site is:- http://www.globaloptimists.org/
I have a copy, with Plus_1 updated to 6.x-2.7, at:- http://globaloptimists.isbd.net/
As you can see the menus at the top are permanently pulled down on the updated site.
Can anyone suggest where I should be looking to see what is causing the problem? It's not urgent as I'm quite happy to leave Plus_1 at version 6.x-2.6 for the present.
-- Chris Green