preupgrade does not find F18

[Frank Zimmermann]

Hi,

I'm traying to upgrade my F17 to F18 with preugrade. However, launching
the GUI leaves me with no options to choose (yes I've ticked "show
unstable test versions") and a
preupgrade-cli "Fedora 18 (Spherical Cow)" 
results in "No version with the name Fedora 18 (Spherical Cow)
available". I've downloaded the releases.txt to folder I'm launchign
preugrade from with no avail. 

Any more hints on how I'd be able to upgrade the system?

Thanks Frank