Please remove FTDI_Ser.dmg from http://beagleboard.org/static/beaglebone/a3/README.htm
This file shuld be removed → http://beagleboard.org/static/beaglebone/a3/Drivers/MacOSX/FTDI/FTDI_Ser.dmg
I strongly reccomend replacing it with a link to http://www.ftdichip.com/Drivers/VCP.htm
As others have noted before the FTDI_Ser.dmg from http://beagleboard.org/static/beaglebone/a3/README.htm doesnt fly with OSX Lion.
Regards
Isbric