[Observium] fresh installation, no login screen

I've followed the installation instructions to the letter, and while I can get to the observium webpage, I can see observium logo and the text "Big Graphs | Widescreen | Not logged in!" on the top right of the page, I can't see anything else. Furthermore, when I look at the HTML source of the page delivered, it ends with " Not logged in!" and not with </HTML> as I would expect.

The machine is a brand new Amazon EC3 VM running Ubuntu 12.04.1 LTS.

I'd appriciate any help. I don't see anything of interest in the apache logs. The same client (browser) works OK for the live demo.

thanks Elad