[Desire HD Q&A, Help & Troubleshooting] actinium15:
Hello echizen81,

Firstly, you must ensure that your phone can still receive fastboot commands. To ensure this, navigate to tools\win folder on AAHK2 extraction location and issue a 'fastboot devices' when you boot to bootloader to see if fastboot works (you should get a entry corresponding to your phone as a result of the command).

If this does, then there's still some hope of recovery! Read on...

On many posts related to AAHK2 issues, senior-forum-members (and Phiber2000 himself) have suggested using brands of SD cards which are known to work. One such list is present here, http://xdaforums.com/showthread.php?t=2367322.

It is possible that your issue could be due to either

a bad SD card which corrupted the transferred zip (since it appears that HBOOT itself was 'downgraded' properly), or

a bad USB connection (which corrupted the zip during transfer), or

a bad flash/hardware (in which case, you'd unfortunately need to buy a new device :( )

I'd recommend you change your SD card before attempting any sort of recovery of your device from this state. Also, make sure that the USB plug stays snug during file transfers. (and keep your fingers crossed while hoping that it is not a device's issue)

I had a similar (not same) issue, wherein I soft-bricked my device due to (incorrect) usage of attn1's AAHK.

Since you can access bootloader, you should be able to use an official RUU (pick an RUU which is supported without downgrade on AAHK2 from here http://shipped-roms.com/index.php?category=android&model=Ace - be sure to pick a Froyo RUU ONLY IF you were using Froyo earlier, else pick-up a GingerBread RUU). However, since misc_version has altered the information an official RUU verifies on your device before flashing, you'd need to use a goldcard.

I recovered my device by creating a goldcard manually and flashing an official RUU. Here are the steps I followed:

acquire another SD card of one of the brands known to work with AAHK2 (Samsung, SanDisk, ADATA, etc)

You'd need to know the CID of the card you are using. Since it is a property of the SD card:

find a device (from a friend, maybe?) in which you can put the SD card

install ES File Explorer (https://play.google.com/store/apps/details?id=com.estrongs.android.pop&hl=en)

read the card's CID register (by navigating to /sys/class/mmc_host/mmc{N}/mmc{N}:{ID}/cid, where 'N' identifies the SD card (in case the device you are using has internal memory as well)

to be sure that you are actually reading the correct CID, repeat the procedure AFTER removing/replacing the SD card

note which MMC ID is absent/changed. This is the ID ('0', '1', or '2') whose CID register you should read and note.

Once you have the CID, visit http://xdaforums.com/showthread.php?p=17247562 for instructions on goldcard creation.

The Gene Poole's http://huygens.hoxnet.com/goldcard.html was working till a few days ago, but is down right now.

If Gene Poole's portal remains unavailable, use the tool in the second post on the thread.

insert the goldcard, ensure your phone is charged more than 30% (if it's not, RUU wouldn't allow a flash. Follow this thread to 'charge' the device to appropriate voltage levels if the 'normal' method of charging won't work: http://xdaforums.com/showthread.php?t=1658084)

Make sure you've all the correct HTC drivers installed. Fire the RUU and your phone should be recognized.

Proceed with flash, and keep your fingers crossed!

Do post your results. All the best!