Yes, i had the problem of not being able to upgrade my X51v.
However i think i managed a solution which worked for me. (Read: -F-O-R- M-E, no flaming the newbie if it don't work for you!).
I tried to update from A01 to A04 on My Intel GERG2 running 2ksp4, and my ABIT-KT7A AMD running 2ksp4 at home. No Luck.
Then I used my brothers Toshiba running XP Pro. Still no luck.
When updating I noticed that the PDA would 'reconnect' to the machine, i.e. the usb bubble would 'detect' a new device from the system tray. Now of course I had the PIN protection system running to prevent 'evil' poeple reading my email, and recall that the PDA won't connect to the PC without this PIN --> and that the message on the PDA when flashing fails is 'Handshaking with PC'. Well most protocols i've studied exchange keys on handshake, and if the program does not know the PIN - handshake fails.
So I simply turned this feature off (disable PIN/Password on power up). BOB's-ya-uncle, flash de PDA.
All is good with the world, MERRY CHRISTMAS.
[now, try not to flame if this don't work 4u]