S6 G920W8 write cert error… new firmware CPG2

A new firmware has been released for the G920w8 and it can’t be downgraded… if you flash an older modem it kills the baseband and imei … any suggestions???
here is the log:

Operation: Write CERT
Selected model: SM-G920W8
Software version: 26.4

Waiting ADB device… OK
Reading phone info…
Model: SM-G920W8
Android version: 6.0.1
Product code: SM-G920WZKABMC
Phone version: G920W8VLU4CPG2
PDA version: G920W8VLU4CPG2
CSC version: G920W8OYA4CPG2
CSC country code: Canada
CSC sales code: BMC
HW version: REV1.0
Phone S/N: RF8GB2Z2S7L
Modem board: SHANNON333
RF cal date: 20151127
IMEI:
Checking Super user right… true
Initializating zTool… OK
Running zTool, please wait…
Start… OK
Init… OK
Generate and check client proof… OK
Verify proof by client… OK
Reading data… error (9)