[U-Boot] AM335x : failure to boot SPL from NAND

I'm trying to diagnose why our AM335x based CPU board (based on the AM335x Starter Kit) can boot SPL and U-Boot from an MMC card, but is unable to boot from NAND (connected to CS0).

Following the TI wiki (http://processors.wiki.ti.com/index.php/AM335x_U-Boot_User%27s_Guide#Flashin...) I:-

(1) boot from MMC (2) erase the nand (3) copy MLO from MMC into NAND (4) verified it copied correctly (using crc32)

When I reboot the board in NAND mode, I get nothing on UART0.

If I reboot in MMC mode, SPL and U-Boot load correctly.

Can anyone give me some pointers on the boot sequence, and where I might look to help debug the problem ?

Regards Mark JACKSON