Thanks Greg, before receiving your reply I could find the problem which was in the insertion to db and I solved it. But now I don't receive confirmation mail so I disabled this feature for now but need to solve email problem as well. I checked the source for sending email and I would like to use sendmail which is default mail server on FC5. Would you please help me to solve email problem as well.
By the way, for your information I changed the following line:
in file: registration.php
changed line:
$sql = "INSERT INTO ".TABLE_PREFIX."members VALUES ('0','$_POST[login]','$_POST[password]','$_POST[email]','$_POST[website]','$_POST[first_name]','$_POST[last_name]', '$dob', '$_POST[gender]', '$_POST[address]','$_POST[postal]','$_POST[city]','$_POST[province]','$_POST[country]', '$_POST[phone]', $status, '$_config[pref_defaults]', '$now','$_SESSION[lang]', $_config[pref_inbox_notify])";
To:
$sql = "INSERT INTO ".TABLE_PREFIX."members (login,password,email,website,first_name,second_name,last_name,dob,gender,address,postal,city,province,country,phone,status,preferences,creation_date,language,inbox_notify,private_email) VALUES ('$_POST[login]','$_POST[password]','$_POST[email]','$_POST[website]','$_POST[first_name]','','$_POST[last_name]', '$dob', '$_POST[gender]', '$_POST[address]','$_POST[postal]','$_POST[city]','$_POST[province]','$_POST[country]', '$_POST[phone]', $status, '$_config[pref_defaults]', '$now','$_SESSION[lang]', $_config[pref_inbox_notify],'')";
Because in your code the value of member_id was 0 which is impossible and since member_id is auto increment, I removed it from insertion.