So you have a Verizon 6700, right? Is the radio ROM you flashed one for Sprint? I've never flashed a different carrier's radio ROM on my 6700, but I did it plenty on my 6600 and it never messed up the phone. I was always able to flash back. Anyway, some questions for you:
1. Are you putting your phone in bootloader before flashing?
2. Are you using the ma_upgrade_noid app to do the flash?
3. Have you tried restarting the 6700 (if you have to, take the battery out and leave it out for a minute or so, then put it back in).
4. Have you tried restarting your PC?
And as a last resort, put your phone in bootloader mode, re-download the latest verizon ROM from
www.utstarcom.com/pcd/downloads (in case the one you already have is corrupt) and run that file as-is (do not extract it or replace any files). If you have a Verizon Apache then that should work. Make absolutely certain that you're plugged directly into a USB port on your PC (no USB hubs) and close all other running programs on your computer. You may also want to try a different computer and/or cable.
It's unlikely that your 6700 is truly bricked. HTC's phones are remarkably resilient when being f'd with. Just keep trying different things.