I upgraded to the latest version of PiWik from version 2.5.1 (??) and the opt-out iFrame is not showing up any more. This is very similar to the issue shown here. I tried:
Copying plugins/CoreAdminHome/templates/optOut.twig to plugins/CoreAdminHome/templates/outOut.twig
Interesting, I am not seeing that error here. I get a blank area that is the iFrames height. When I view sorce in Firefox and click on the iFrames source link I see the page I am expecting. I tried adding &idSite=0/1/talkingcouch to the frameset but it didn’t do anything. Where do you see that error?
I am also a little unsure what you mean by:
Additionally your site seems to block the forwarding - so your cookie-policy is still readable (unlike mine sad smiley )