http://www.mediafire.com/?btziywycomz
i got a AU-HK v1.70 UMS firmware. i alway back up by copy and paste the firmware file before unplug the usb cable for firmware upgrade.
i using a T10 256mb. think this v1.70 can be use for T10 256mb, 512mb and 1GB but NOT the 2GB version.
those interested can download from the link and try downgrade but do it at your own risk, i just trying to help.
http://www.iriver.com/html/support/d...pSearchString=
or you want go down to lower version like v1.51. you can find the firmware at iriver.com.