sorry man, i don't even know if it is uboot who complains. i only know that uboot has such a errormessage if the uImage is somehow corrupted(cant read, execute it). thats the hint i can provide you.

its a huge ext3 partition with everything on it.
if you want to make it work with ali's uboot patch: that looks on the third partition if it can find something to boot(therefore you need a 3 partitions: the patch is such that it looks at the 3rd part and only if it is a vfat).
- first it looks for a boot.scr which holds the information how to boot. if so it executes the comands in this file.
- if it cant find the boot.scr it falls back and tries to fetch a kernel from this same partition and boot iirc the first partition with that kernel.
- if it can't find that it falls back to boot with nolo's settings boot(that is maemo unless one has tempered with nolo).