Well I've just been pissing about the last couple of hours trying to get an SDHC card working on a TomTom One v2 I bought someone for Xmas and finally got there!

Basically you need to upgrade the bootloader to 5.5022 or above - currently using the Home software with the latest updates for these they still don't support SDHC cards.

Easiest way to do this is as follows.

Download this file I just upped:

[Only registered and activated users can see links. ]

Mount the TomTom UK + IE card that came with your TomTom in Windows or Mac.

Copy the file you just downloaded named SYSTEM to the root of the TomTom SD card, ie if your TomTom SD card is mounted as I: ensure that you copy it to I:\ in Windows Explorer or the command prompt.

Unmount the drive cleanly using the Remove Hardware Wizard

Put the card in the TomTom One and reboot - upon next reboot it will flash the bootloader with the system file - you can check this by looking at the versions of the software when it comes up - it should show:

Boot: 5.5022

That's it - your TomTom One now supports SDHC cards so you can stick in your card and it will recognise it and boot from it

Hope this helps anyone out there that gets stuck like I just did as I didn't have any none-SDHC cards lying around apart from the standard one