Lpc2000

>Random guess. Power supply sequencing and SCR latchup internal to the
part.

Bill, 

this is the exact source of the problem!
adding 47uF capacitor to the +3.3V LM1117 removed the problem, it 
seems that for whatsoever reason on these boards +3.3V rises faster 
than +1.8V and this latch up LPC2106.
On all our future boards we'll put 10uF to +1.8V and 47uF to +3.3V 
regulator thus will ensure some delay on +3.3V.

this explains why these boards started to work when +3.3V vreg was 
working to +2.5V with insufficient Vin - in this case the output of 
+3.3V vreg rises slower and ensure the correct sequencing.

Best regards
Tsvetan