How did you unlocked your device?
If the htcdev unlock method was used, than you can not flash boot.img since it is still locked.
Check this thread:
It is compatible, I flashed firmware, tried 4.0.3, then returned to CM7.1 and everything is working well
check your drivers, i assume you are on 64bit Win7, I had similar problems on my win7x64 OS, then I switched to a 32bit XP, installed drivers, and everything went well
hope this helps