R3 Device Signature Error

Still no luck with 328P-PU device codes. I tried everything I can of. I ran the Loop-Back test and it checked ok. I have run several sketches with serialWrite and digitalWrite with success. But, every time I try to upload a hex file for my CNC project, I get:

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.01s

avrdude: Device signature = 0x000000
avrdude: Yikes! Invalid device signature.
avrdude: Expected signature for ATMEGA328P is 1E 95 0F

This is the instruction I sending the board via the Mac Terminal.

/Users/myUserName/Ardunio/build/macosx/dist/tools/avr/bin/avrdude -C/Users/ myUserName /Ardunio/build/macosx/dist/tools/avr/etc/avrdude.conf -pm328p -cstk500v1 -P/dev/tty.usbmodem411 -D -Uflash:w:grbl_v0_8b_edge_328p_16mhz_9600_build20121013.hex –F

Desperately need help to keep my project going. Thanks.