I have a 2002 Silverado 6.0l and had the same problem you are having. Going through these forums, Is seems this is a very common problem. I installed this tuner in my truck at the Summit Racing parking lot. After not starting, I had to have it towed to the dealer. The tech could not communicate with ...

It would appear that your PCM is cleared off.
Unless you physically caused the tool to stop writing (turned off the key or unplugged the unit while writing) then you must have had a low voltage situation.
The PCM likely needs to be reflashed. This can be done at any GM dealer or if you would like ...