Arduino+Firmata looses connection after approx. 1 to 5 minutes

I use a Arduino Diecimila and the Firmata 2 beta 3, uploaded with Arduino IDE 10. (as described here: arduinofirmata
Everything works fine, but after approx. 1 to 5 minutes, I loose all connections with the Arduino. All DigitalOutputs reset to 0.
Then, when I quit v4, unplug the Arduino and plug it back in, everything works, but again only for 1 to 5 min.
Am I doing something wrong?
Is this a known bug?