Check the download ed .rar file for integrity
remove all files from your SD card
copy the firmware files again
try to flash again.
Today Haipad released a new Android 2.3 firmware by the way:
????--www.haipad.net
[mirror]
My suspicion would be that something with your flash memory or the internal SD card is wrong.
As i said, i never seen that happening and it is amazing that everything seems fine until you unlock the screen =(