[support] D6: Anonimous comment are not displaied

Hi all. I have this strange problem with my drupal 6 installation (www.ziodrupal.net): anonymous comment are not displayed. Anonymous can send comment and comment are writer to DB (I can see it in the comments and node_comment_statistics tables), but not displayed in the node's page. I have checked the permission and seems correct to me. If you see this page:

http://www.ziodrupal.net/links/prova-di-inserimento.html

You can see "2 comments in reply to prova di inserimento" and infact in the db there are 2 comments, but only the one of "admin" user is displayed. I have tried with my theme and with "garland" theme, but the results is the same.

Any help is welcome.

M.