latest version of this plugin is 22.214.171.124 ( http://wordpress.org/extend/plugins/audio-player/ ) and wordpres audio module inside SWF tools doesn't match the new player path:
path is now: /sites/all/libraries/audio-player/assets/player.swf
audio module search for: sites/all/libraries/audio-player/player.swf
I had similar issue with "1 pixel out" and also for "JW Media Player 5" (see http://drupal.org/node/887956 ) new path: I think SWF tool have to manage better path upgrades, giving the possibility to change paths trough admin.
Thank you very much