An update has been released and is available on Finale's website:

http://makemusic.custhelp.com/app/answers/detail/a_id/1720

This Garritan Aria updater is a free, downloadable update available to registered Finale 2010 Macintosh users. It provides compatibility between the Garritan Aria player (included with Finale 2010) and Macintosh OS X 10.6 (Snow Leopard) and 10.7 (Lion). An account on finalemusic.com is required