Hi
we've had the same problem on R80.20, just solved it.
You must rename your managemet server, hostname must not start with CP_MGMT, either lower or upper case.
Go to expert mode and execute "more $FWDIR/log/fwm.elg". You should see the following message:
write_using_CPMI_and_add_to_downgrade_hash: Update failed: Illegal name for 'CP_MGMT_R80' @ 'network_objects' - Object name can not start with 'cp_mgmt'
We changed hostname to something else (originally ours was CP_MGMT_R80 as you can see in the message above), rebooted the managemet server and it solved the problem. It took some time for server to start, even after "cpwd_admin list" showed all processes in E state (executing).
Best regards