Sounds like you have not burned the disc correctly, try this
Once you have downloaded the file, unzip it (using winzip or similar) into a sub-dir on your pc.
Then use imgburn or similar (
http://www.imgburn.com/index.php?act=download) to burn a new
(blank) cd with the new downloaded firmware image.
eg:
install imgburn.
then run.
open v29.mds (from sub-dir).
select "mode write" from menu.
press write (cd image at bottom).
Burn at 1x speed, on good quaility cd.
When its finished writing your new firmware cd,
Goto the car open the drivers door,
Goto the dvd nav computer wait for the red led on the drive to go out,
Then press eject on drive,
Eject the map disc,
Switch ign to pos 1, leave door open.
Insert firmware disc into drive, follow instruction on nav screen.
Wait (approx 6 mins) till sat nav asks to eject cd and reboot.
Eject cd,
Confirm reboot.
Thats it.
Do not swich off ignition or close the door when doing the upgrade.
Hope this helps.