ANONYMOUS I've the same problem. Try to use "Pacifist" software (http://www.macupdate.com/info.php/id/6812). You will be able to read your package and install manually the driver. (Version 1.8)
GUBDEB Hmmm... but I don't have either of my Keyspan devices connected... Maybe it has a problem with ANY USB device? A scanner/printer/Modem and imate USB/ADB convertor are present on mine. (Version 1.7)
BVL I remembered that trouble occurred the first time I installed a Keyspan update driver, since I often don't read the caveats before I install...you have to disconnect the serial device before you install the software or you'll get a kernel panic. No problems at all that way (OS X 10.2.8). (Version 1.7)