[Plugin: WP-Affiliate] plugin doesn’t work anymore with WP 2.8

I have found that the problem is with this line :

wp_print_scripts( array( ‘sack’ ));

When WP-Affiliate adds the SACK js lib to the page, a bunch of JS errors appear. Is there an incompatibility with SACK and 2.8, it does come with WP 2.8, should I use the .dev version instead?

add_action('admin_print_scripts', 'wp_affiliate_js_admin_header' );

function wp_affiliate_js_admin_header() // this is a PHP function
{
  // use JavaScript SACK library for Ajax
  wp_print_scripts( array( 'sack' ));

  // Define custom JavaScript function
?>
<script type="text/javascript">
//<![CDATA[
function wp_affiliate_ajax_add_link( link, text, category )
{
   var mysack = new sack( "<?php bloginfo( 'wpurl' ); ?>/wp-admin/admin-ajax.php" );    

  mysack.execute = 1;
  mysack.method = 'POST';
  mysack.setVar( "action", "wp_affiliate_add_link" );
  mysack.setVar( "link", link.value );
  mysack.setVar( "text", text.value );
  mysack.setVar( "category", category );
  mysack.encVar( "cookie", document.cookie, false );
  mysack.onError = function() { alert('Ajax error in adding affiliate link' )};
  mysack.runAJAX();

  return true;

} // end of JavaScript function
//]]>
</script>
<?php
} // end of PHP function myplugin_js_admin_header

This outputs the following:

<script type='text/javascript' src='http://bloguedegeek.net/wp-includes/js/tw-sack.js?ver=1.6.1'></script>
<script type="text/javascript">
//<![CDATA[
function wp_affiliate_ajax_add_link( link, text, category )
{
[...]

I have this same problem, its stopped working now soon after I upgraded. Old links that were already saved are working but any new links show 404 error.

I tried permalinks suggestion above, but doesnt work. I use custom structure:

%postname%

Could you be a bit more specific? What file needs 666 permission?