can not write cert file on g925f s6 edge

Any idea how to fix this issue?
i can not write ant cert file on s6 edge g925f on android 6.0.1
and can not downgrade it to earlier vision i keep getting
Reading data… error (8)

Operation: Write CERT
Selected model: SM-G925F
Software version: 27.1

Waiting ADB device… ok
Reading phone info…
Model: SM-G925F
Android version: 6.0.1
Product code:
Phone version:
PDA version: G925FXXU4DPH1
CSC version: G925FOLB4DPH1
CSC country code: VIETNAM
CSC sales code: XXV
HW version:
Phone SN: R58G819…
Chip name: EXYNOS7420
Modem board:
RF cal date:
Checking Super user right… true
Initialization zTool… ok
Running zTool, please wait…
Start… ok
Initialization… ok
Generate and check client proof… ok
Verify proof by client… ok
Reading data… error (8)

Done with Samsung Tool PRO v.27.1


  • Reading data error (9) cert g925f