This is the picture James wanted to publish:



James, I miss the two 27pF burden caps arround crystal. Also, crystal looks like low-profile HC49. Try a standard HC49 package instead. Keep the connections of oscillator parts as short as ever possible!! Each millimeter counts...

Some decoupling caps are missing (unless they are mounted on the solder side): 100nF cap across output terminals of 7805, 100µF/25V electrolytic cap across input terminals of 7805 and 100nF cap across supply pins of micro.

And: Without solid ground plane benefits of decoupling measures are only little. Try to avoid 24MHz, try somewhat lower clock frequency.

If you want to omit the obligatory reset chip, connect at least a discharging diode across electrolytic cap of RC-reset circuit and choose a somewhat bigger capacitance for this cap.

I can't see it right, but I guess the GND connections of your board should be much much wider! Can you try to make a double sided board containing a solid ground plane? This would hugely help!

Kai