Hi,
first sorry for my english, i'm catalan, from Catalonia.
Well, I have a problem when clic in a categorie of my blog (www.rodon.cat/blog_nocturn). A message appears with
Fatal error: Call to undefined function is_last_post() in /home/jrodon/public_html/blog_nocturn/wp-content/themes/atahualpa/archive.php on line 32

Thanks

Are you running Atahualpa 2 or 3? Version 3 doesn't have an archive.php anymore, but if you had Atahualpa 2 in that directory and uploaded Atahualpa 3 into the same directory then this kind of error would happen.