Welcome!
This can occur during an attempt to program the PCM after installing the Gryphon in the vehicle.The Gryphon will detect if the PCM is stock or not, and if it is NOT stock then it will stop dead in it's tracks with a checksum failure. This problem can also be caused by a missing "stock" file.Contact PHP to restore the PCM to stock or to download the missing stock file.
In other words you may have on nonstock program on your pcm.
There is another thing you need to look at also to see if you have custom tunes still loaded on the Gryphon. I'll be back with that.