error dialog not centered

[Beast <beast ldap or id>]

I have these following code:

...

sub cb_ok {
   my $self = shift;
   ...
   my $dialog = Gtk2::MessageDialog->new($self, 'modal', 'error', 'ok', 
$message);

   $dialog->set_position('center-on-parent');
}

But it behave like I wanted.

1. The error pop-up did not center in their parrent, but seems on 
top-left of screen.
2. How to make the "OK" button centered (presently it right alignment)?
3. How to remove the icon on the "OK" button?


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--beast