I've installed: Joomla 1.5.9, Joomfish 2.0.1 (including bugfix) and Artio Joomsef 3.2.3.
I'm using four languages, the third is italian.

With joomfish and on the homepage it's possible to switch to 3 out of 4 languages without problem.
When you select italian you get a 404. When you insert the old URL for the italian homepage it works.
On the testserver there where no problems.

On other pages everythings works properly. Does anyone have an idea. We've alreday cleaned cache, inserted the working old URL manually and removed the URL from jos_redirections, with no effect.