No Partition Found (64gb SDXC card)

[Gaz_m2k5]

I have modded my iRiver H120 with a CF card reader, and got the adapters to put a MicroSD in.

With a 2GB SD card, it was fine, booting from ROM.

Now that I have the 64GB MicroSD card, it says No partition found when I boot from ROM.

If I choose to boot from Disk, it says the same thing, but if I then press the reset button on my player, it boots up fine.

I have formatted the device and checked that the partition id is 0x0B.

Very frustrated now.