Oracle Forms

First of all i wud like to congrats the gurus and others for taking interest in solving many issues.

I have created a logon form where i have put username and password with the connection database.
(i.e)
LOGON(UN,PS||'@'||'sample',false);
if form_success then
call_form('example.fmx');
else
message('please enter valid input');
end if;

but when entering wrong password and user name it still call the indicated form.
i wonder how the form_success becomes true,
suggest me a solution.

With regards,
Naresh Kumar Murali