Samsug G920w8 write cert failed/ exploit failed

help need ?

Welcome to Octoplus/Octopus Box Samsung software version 2.3.8
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To connect SM-G920W8 phone you have to perform the following
steps:
1. Disconnect USB cable from phone.
2. Go to Menu->Settings->More->About Device.
3.Tap on "Build number" 7 times to enable developer options.
4. Go to Menu->Settings->More->Developer options.
5. Turn on "USB Debugging" option.
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Platform: Samsung Android
Selected port: COM2
Selected model: SM-G920W8
Searching for a phone. Please wait…
Phone found.
Detected phone model: SM-G920W8
Firmware compiled date: Mon Jul 11 22:32:37 KST 2016
PDA version: G920W8VLU4CPG2
CSC version: G920W8OYA4CPG2
SW version: unknown
Phone SN: RF8H72EQQLA
Android version: 6.0.1 (MMB29K)
Sales code: VMC
Country: Canada
HW platform: exynos5
HW Chip: exynos7420
HW Modem: unknown
Codename: zerofltebmc
Performed by 2.3.8 Software version.
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Platform: Samsung Android
Selected port: COM2
Selected model: SM-G920W8
To put SM-G920W8 into Download Mode, You have to perform the
following steps:
1. Reconnect the battery.
2. Press and hold "Volume-" + "Home" + "Power ON" keys.
3. When phone turns on, press "Volume+" key.
Repairing EFS…
Searching for a phone. Please wait…
Phone found.
EFS Repair successfully
Performed by 2.3.8 Software version.
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Platform: Samsung Android
Selected port: COM2
Selected model: SM-G920W8
Selected file: C:\Program Files (x86)\Z3X\Samsung\SamsungTool 20 3
\backup\Cert\SM-G920W8_RF8GA2G4W9V_351559*******
GOOD.cert
Detected phone model: SM-G920W8
Firmware compiled date: Mon Jul 11 22:32:37 KST 2016
PDA version: G920W8VLU4CPG2
CSC version: G920W8OYA4CPG2
SW version: unknown
Phone SN: RF1D45EJGGR
Android version: 6.0.1 (MMB29K)
Sales code: VMC
Country: Canada
HW platform: exynos5
HW Chip: exynos7420
HW Modem: unknown
Codename: zerofltebmc
Checking Root:
Phone is Rooted.
Reading security backup, please wait…
Backup saved as C:\Program Files (x86)\Octoplus\Octoplus_Samsung
\BACKUP\Security-SM-G920W8-Unknown18-10-2016_18-01-17-.asec
file
Checking Certificate file…
Certificate file successfully checked
Deactivating MSL…
Executing exploit…
Executing exploit failed
Writing Certificate failed
Performed by 2.3.8 Software version.