Arduino Clone is not talking to my Mac
OSEPP has (purposely) mislabeled their boards/products.  It is not an Uno.  It has a FTDI chip which requires drivers from FTDI.  Additionally they usually have the Duemilanove bootloader installed instead of the Uno bootloader, requiring you to select Duemilanove in the board menu.

You can download the FTDI drivers from here:
http://www.ftdichip.com/Drivers/VCP.htm