I found this thread after search for an message that I saw for the first time today: "Internet Explorer cannot download blocker.swf from localhost". My installation of Avant is the latest, I always update as soon as new version is available.
The subfolder "imgs" was present and contained a file called blocker.swf. There is also a subfolder called "res" that contains a file called blocker.swf. Following the advice in this thread I deleted the imgs folder and the problem message no longer appears.
My configuration has been the same for some time and I suspect that what changed was something on the site I was viewing, www.telegraph.co.uk.This
is a very badly managed site seeming to be thrown together with great haste and very little checking. Several times a week something is wrong with it, broken links, duplicated entries, links that take you back to where you started, items missing and so on. Worst of all are the intrusive, insistent and annoying advertisements. The content is great which why I use it but the people who control the site are not in the same league as www.bbc.co.uk
, whose site is just as frequently updated but is managed by skilled web controllers.
My uneducated conclusions? Firstly, the Avant installation routine should delete the leftover imgs folder. Secondly, there are some rubbish built sites that would throw the best written browser, so don't always blame Avant first (but a check doesn't hurt!).