This happend to me also. If you followed the particular guide I used on how to S-off/root/install recovery, it says to run 'fastboot flash boot recovery.img'. It should say 'fastboot flash recovery recovery.img'.
I just flashed a ROM and that fixed it.
Yeah I seen a few posts of ppl saying xxxxxx I'm not going to say it! Your correct,
1. Install drivers (no HTC sync)
2. Unlock bootloader via htcdev.com
3. Download recovery image (Rename recovery.img)
4. Grab fastboot files with adb
5. From a command line,
adb reboot fastboot
fastboot flash recovery recovery.img
fastboot reboot
6. Use firewater for S-Off
This is just what I recommend. This is the short version
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