Been banging my head off a wall all day wondering why SWFAddress 2.1 wasn’t firing on initialising. The answer is pretty simple – you HAVE to make sure you include “id” in the optional attributes or it just won’t work. Here’s what I had (wasn’t working):

swfobject.embedSWF("darey_v2.swf", "flashContent", "100%", "100%", "9.0.0", "assets/swf/expressInstall.swf", null, params,null);

and it didn’t work… but I changed it to this:

swfobject.embedSWF("darey_v2.swf", "flashContent", "100%", "100%", "9.0.0", "assets/swf/expressInstall.swf", {}, params, {id: "dareysite"});

… and its all sweet – note the extra {id:"id_goes_here"} bit as the last argument to the static embedSWF function.