freeze after programming image to mx28

Dear Sir,

I have got a problem after programming wi-imx28 board.
I had successfully already use this procedure with some board and not with 2 new item.

After booting on U-boot:
setenv serverip
setenv addrip
ping (successful)
update uboot tftp
update linux tftp
update rootfs tftp
setenv bootcmd dboot linux flash

Up to this step every thing looked like working as usual

And after typing ‘reboot’, the part freeze and impossible to reboot.

Does any body have an idea ??

Thank’s a lot

Saint-Emilion (France)

Refer Digi ESP >Help> Help Contents > Digi ESP for Embedded Linux > 16. Recovering a device 16.2. Loading a boot loader via USB