Errors in connecting an Arduino to Ros Groovy

I'm trying to get an Arduino Uno hooked up to Ros Groovy; I've been following the Hello World tutorial for rosserial_arduino. When running >rosserial_python serial_node.py /dev/ttyACM0 I'm able to connect for a second, and I start getting the error: > [ERROR] [Walltime: ...] Lost sync with device, restarting... I noticed my Arduino code is still running even though it lost connection (I have a flashing LED indicator). Its not publishing anything to "Chatter" however - not even once before it disconnects. Please let me know how I might be able to fix this! Thanks!