Disable Raspberry Pi Serial Console
see more information on the official raspberry pi forum. Long story short, when the pi boots, its sends data on the GPIO, some of them are connected to the rapiro don't play well with each other..
and with that script, you can easily enable or disable the serial console.
installing the script
just copy and paste this line into you terminal console
sudo wget https://raw.github.com/lurch/rpi-serial-console/master/rpi-serial-console -O /usr/bin/rpi-serial-console && sudo chmod +x /usr/bin/rpi-serial-console
the script is now installed on your PI.