Eclipse + avrdude problem

I'm trying to program the Arduino using Eclipse. I followed the guide for setting up Eclipse on the Arduino website. Everything compiled correctly, but when I tried uploading to the Arduino I get this console output:
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude finished

The program downloads fine using the Arduino IDE.
What could be causing this, and how can I fix it?

Sorry the forum would not let me post a link. This is the guide I used: Arduino Playground - Eclipse