Hi guys, thanks for your answers.

I followed the sugestion of Mr. Ballinger. I have created the database with Pgaccess. This utility (or postgres itself)create a set of database properties within the database, so I look for this catalog and found the file pg_database. One of the fields is "Encoding" it was set to 1 and this number correspond to the ASCI encoding I change this value to 5 (UNICODE) and all the rest work fine. The problem goes away.

Thanks again, and regards.