I have discovered a working solution for people that have S-OFF RELOCKED and took the latest/last OTA update but cant flash a recovery via fastboot and cant re-unlock.
When i tried the following in fastboot
fastboot flash recovery recovery.img (place your favorite recovery into platform-tools folder)
< waiting for device >
sending 'recovery' (8758 KB)...
OKAY [ 1.018s]
FAILED (remote: not allowed)
finished. total time: 1.049s
It errors out by using TWRP and CWM FAILED (remote: not allowed)
download the attached recovery.zip and place it into platform-tools (TWRP recovery)
fastboot oem rebootRUU
---wait for black HTC logo--
fastboot flash zip recovery.zip
--it will show a progress bar on your phone, and finished in the CMD window--
fastboot reboot bootloader
Can someone confirm that flashing recovery works with the method above. Also post what version software you are running. Someone with S-ON LOCKED please try this, possible new way to flash ROMS without S-OFF/unlock?