Gtk and Glib::Timeout

I am writing a program in perl which invokes a small window. This window
should time out after some time. For the window I use Gtk2. For the
timeout I use Glib::Timeout

The code looks something like this:

my $dialog = new Gtk2::Dialog( );

(creating some buttons and all)

my $timer = Glib::Timeout->add( $interval, \&some_func));

Gtk2->main;


This returns Not a CODE reference at /program_path line line_number

Should I use Glib (and how?) or is there any other function I should use.