OS X V10.5 Leopard :: Disk Image .DMG Unable To Mount / Attach - Not Recognized?

After a fatal mac crash (PPC 10.5) i had no option but to reinstall the OS (10.5), i obviously didnt reformat the drive in the hope that i would be able to recover some if not all of my data. Using various tools i was happily able to recover most of my data successfully, including 3 AES encrypted Disk images of around 30GB in size each.

I didn't hold out much hope for actually recovering the data inside the dmgs, although after some fiddling i was able to recover 2 of them fully after receiving the no mountable file system error, i dont know how i done it but nonetheless i dont appear to have lost any data from those two dmgs whatsoever. Now the third dmg (also about 30GB in size) never gave me the no mountable file system error and instead returns the error: unable to mount: not recognized. Im pretty sure that my data is still there somewhere due to the sheer size of the recovered file, tied with the fact of the success of the recovery of the other 2 disk images. I have read every post i could find on this site and have trawled the web tirelessly looking for a solution to this, but have yet to find anything that even comes close - the closest i have found was a post on this forum where it would appear an apple engineer was able to recover most of the data using some sort of magic.

I am not in a position to pay for professional data recovery and besides i would love to see a solution to this problem appear somewhere on the web. I have tried the usual, rebuilding permissions, mounting on another machine (imac G5), resizing with disk util, repairing with disk warrior, converting to ISO - all which return the same error - not recognized! I have tried every terminal command i have found on the web, although decyphering some of the information is a little out of my remit and my knowledge of HEX is limited. I haven't yet tried Toast, basically because i dont have a copy, but it would be my guess that this would return a similar result. Incidentally when i recovered the original data, there were some small (what appeared to be dmgs) files around only maybe a few Kb each with part of the file names of the original files, i'm guessing these maybe the headers or something like that? although i didn't have to do anything with them to get the other 2 disk images working again.

Info:
iMac, Mac OS X (10.5), Disk Image error