[support] Strange behavior of upload in drupal.js

Hi all, I've got a multisite installation of drupal 5.10. In the main domain, when adding an item via upload form (or imagefield) the server give me back an error keeping the animation running. The #redirect-target has inside the json data but trought firebug I get a "data is null" referred to line 131 of drupal.js This is caused I think by this line (about 56) /response = (iframe.contentWindow || iframe.contentDocument || iframe).document.body.innerHTML; /that say (from console.log) "Permission denied to obtain the property Window.document" This happens on various browsers and only in the main site (upload in subdomains works well). (maybe a theme related error?) Did somebody ever had a similar problem ? Cheers, Lu