I flashed the nand with a RouterBoard kernel version 3beta7 image that contains
a 2.6 GNU/Linux kernel. This procedure formats the nand before doing the
flashing. The patched 2.6.19.2 kernel can not read it, gives errors but it
doesn't hurt the data since we can boot from the nand on the next cycle. . Here
is the nanddump -ni /dev/mtd0 resulting of this:
http://wifi.ozo.com/airo/openwrt/rb1xx/debug/rb_kernel_dump.bz2

Next, I formatted the nand from the RootBoot bios, netbooted a patched 2.6.19.2
kernel, wrote the patched 2.6.19.2 kernel to the nand which gives a working
result since the RootBoot loader can then boot that kernel.  nanddump -ni
/dev/mtd0 results are here:
http://wifi.ozo.com/airo/openwrt/rb1xx/debug/wrt_kernel_dump.bz2

I am suspecting that the RouterBoard tftp flash uses a differnet nand format
compared to the RootBoot loader format. A tcpdump may or may not reveal some of
the magic involved on this ...

Obviously, the RootBoot loader can read both formats.