One user ECUHELP feedback:
After testing KTflash Exx Series module these are the results:
-E39 Reading ok, writing ok
-E39A Reading ok, writing no, blocked
-E37 does not read, does not write, blocked
-E38 does not read, does not write, blocked
-E82 does not read, does not write, blocked
-E92does not read, does not write, blocked

ECUHELPshop engineer advice and suggestions:
1. Check if the cable is good or not, the software is surely no problem.
2 . Take a photo of the error message to help us guide you how to do next.

Finally:
I fixed the E39 ecu that had locked up. I blocked the ecu and had to recover using IO Prog in boot mode.
10 tests were performed with 14V, all of which failed, blocking the ECU 8 out of 10 times.
With 15V it read and wrote without errors in all 10 rounds.
Please note when using KT flash on Delco Exx ecus 15V DC/5A and it will write safely.
Otherwise, it is easy for the ecu to lock up.

KTflash E38 read write on Bench, DTC OFF ok: