Found a solution in the old Arduino forum!

Answer:

"I had the same problem, using an older mac with an arduino uno. I found that if I hold down the reset while plugging the usb cable into the arduino, with the computer already on that this solves the problem...

The pain is that you will have to do this every time you want to upload a new program, better than not working at all. "

Link:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1287015838

Hope that helps somebody.

Hi:

I am trying to program my Arduino Uno for the first time using the "Blink" sketch in the examples folder, but when I try to upload the sketch, I get the following error:  avrdude: stk500_recv(): programmer is not responding.

This happens when the upload bar gets to about 90% complete.  I am also able to see the RX LED on the board light up, but not the TX.  To my knowledge I have selected the proper board and serial port from the "Tools" menu.  I am running Mac OS X 10.5.8.

An image of the error is attached as a PNG, but let me know if more information is needed.  I haven't been able to find anything that resolved the issue in the forum or FAQs.  All help is appreciated...Thanks.