[Jim E]

Speculation:

Hmmm. Having not seen the board yet, It does appear a problem exists with the 5V regulator load.

One could measure the resistance between the output pin of the regulator to ground to determine if a short is there before power is applied.

Look the board over closely before applying power. Use a magnifying glass or microscope. Make sure the solder connections are good and sound. A good lead-free solder connection will appear slightly grainy. Any connection a dull, bumpy gray is suspect. Also check to make sure the pins are actually making contact to the pads. Sometimes it looks good, but oxidation or lack of flux will cause an open connection.

Lead-free (RoHs) solder does require higher temps in the reflow oven. Many companies are scrambling to overcome this obstacle. If the part is not designed for RoHs solder techniques, it may not survive. National Semiconductor's new stock has been RoHs compliant for years.

Hopefully, the problem is not in the PCB traces themselves. A short in adjacent traces will be impossible to repair if it occurs in internal PCB layers.