jQuery HoverIntent is not a function

According to the wp_register_script() Codex the first parameter handle should have a unique name.

If we look at the paramters of the wp_register_script() function it breaks down like this:

wp_register_script( $handle, $src, $deps, $ver, $in_footer );

So your wp_register_script() function should also break down into a similar way:

wp_register_script( 'dropmenu1', get_bloginfo('template_directory') . '/js/jquery.dropmenu.js', array('jquery'), '', false);