Trouble switching language

Hi,

I can’t seem to find any other treads, if so please point me in the right direction.

I have a site in danish, and would like to translate it to English. I have translated my frontpage, translated strings, etc. I have added language switcher to my menu. Everything seems to be running. However, when I click the british flag in my menu, I get an 404-error, saying “The requested URL /en/ was not found on this server.”
Can anybody locate what I am doing wrong?
I have a test site which I put up first (www.sokuno.dk/wordpress), with the exactly same setup, and there the translate switcher works perfectly. I have been through all my setting, and the only difference I can locate is a #primary-string missing – which I don’t know how to add.

Any help would be very appreciated.

The page I need help with: [log in to see the link]