Thank you very much for you help again, Ryan. Afther a long research, I found the answer in the link that you gave me. I've changed the following line in the search-users.tcl file:
ns_write [encoding convertto utf-8 $response]
I'm forcing the encoding to be utf-8. It seems to me like ns_write is ignoring the server's encoding (possibly an AOLServer bug). In your standard exit:
ns_write $response
the HTML response to the browser gets the wrong encoding, but the ns_log command, for example, has the right server encoding. It's an workaround but it's working.