Edit Article auto redirect to preview article

I use wp 2.1.1 fresh install on a RedHat EL 4.1 system.
when I click modify article wp shows modify page for a second and auto redirects in preview article page.

I mean:
I click http://comunicazione.lettere.univaq.it/wp-admin/post.php?action=edit&post=66
and I get after a second
http://comunicazione.lettere.univaq.it/?p=66&preview=true

Can you help me?
thnks in advance
fabrix