Attached to the Arduino, I have six relays connected to outputs 2 to 8.
Do you use transistors to switch the relays? The outputs only can deliver 20 mA per port.
hese outputs are HIGH for at most 30 to 60 milliseconds and I access them at most 20 times per second.
Do the relays switch correct? It seems that the signals are to fast for relays.
Please check you power supply. May be the power regulator switches the power off because of to much power consumption.