What type of oscillator circuit are you using. It sounds very likely to me that your oscillator is not starting reliably. It could be a matter of your crystal not being loaded with the proper capacitance or improper PC board layout of the crystal wiring to the microcontroller pins.

You should also be aware of Analog Device's errata sheet for this device. There is an issue that will, upon end of RESET cause the part to go into an "internal emulation" mode. That may be what is happening to you!Go to the errata sheet at:

http://www.analog.com/productSe...df

...and look at the final item. There appears to be a workaround by putting a pulldown resistor on the PSEN line.

Good Luck
Mike Karas