error read codes g935a

hi i am trying read codes to g935a and downgrade modem this is log
please help me


Operation: Read Codes via Server
Selected model: SM-G935A
Software version: 33.8

Checking Login and Password... OK
Ballance: 5 crd.
You have 5 credit(s) left. This operation takes 5 credits.Continue? Yes
Waiting ADB device... OK
Reading phone info...
Model: SAMSUNG-SM-G935A
Android version: 6.0.1
PDA version: FA60_G935AUCU4AQB1
CSC version:
Phone version: G935AUCU4APK1
Product code: SM-G935AZKAATT
CSC country code:
CSC sales code:
Phone SN: R38H20QY42A
IMEI: 357216070871489
HW version: REV0.7
RF cal date: 2016.02.25
Chip name: MSM8996
Modem board: MSM8996
Security patch: 2016-01-01
Boot Warranty bit: 0
Rebooting phone... OK
Waiting ADB device... OK
Waiting for device to become ready... OK
Initialization zTool... OK
Running zTool, please wait...
Start... OK
Initialization... OK
Generate and check client proof... OK
Verify proof by client... OK
Reading data from phone... OK
Searching Ramdump interface... COM8 detected
Reading data from phone... OK
Calculating... OK
Searching server... OK
Waiting for server answer... error (1)
Done with Samsung Tool PRO v.33.8