There are a few things that can cause the sketch uploading to fail. First verify that you selected the right COM port. Sometimes people are having trouble when using double digit COM port. If the right port is selected and you are still having problems. Restart your computer and your Galileo. Keep in mind that Galileo takes a couple of minutes to completely boot Linux and within this time the sketch might fail to upload. Can you can upload a simple sketch like the “Blink” example? If that fails try clicking the “Reset” button on Galileo (next to the SD card) a couple of times then try to upload. Also what Linux image are you using?