wilykat:
Are decoupling capacitors present on VCC to GND near the chip's VCC pin? Without those caps, the voltage rail can ripple a bit and cause the chip to become a bit finicky.I'd recheck for bad solder join on the Rx, Tx, reset, and all VCC and GND pins.
Yes they do have decoupling caps 0.1uf to GND on Pin VCC and AVCC