I saw this issue performing an upgrade readiness check from FMC on FTD. FMC was in HA deployment (Active/Standby pair).
Other FTDs completed readiness checks successfully so it was not related to file corruption.
This bug was also not related as FTD registration to both FMCs had been completed.
Upgrade readiness check from CLI completed successfully. The command to execute this check from CLI is below (push upgrade file from the FMC first).
install_update.pl –readiness-check /var/sf/updates/Cisco_FTD_SSP_FP1K_Patch-6.7.0.3-105.sh.REL.tar
After bouncing around in the logs I noticed that FTD was showing Offline on standby FMC and SFtunnel was not establishing.
In another case I saw ChannelA connected but ChannelB down.
Resolving the SFtunnel connectivity issue cleared Offline status on standby FMC.
When the issue was resolved upgrade readiness check completed successfully.