Hi, I've looked at the sites. I manage to repoduce the error if I entered the "/edit" area with an url not starting with "www". Doing this can cause the preview to not function properly.
The quick workaround is to make sure you enter the "edit" mode with a url that matches one of the primary domains of the site. In the "styreinstitutt"example, use: http://www.styreinstitutt.no/edit not http://styreinstitutt.no/edit
In a furtue update, we'll change the preview so it work as expected regardless of the URL you use. It's high up on the list, so expect a fix for this before 01.10.2011