I recently installed UML on my ubuntu machine and it worked great. However i download a linux kernel(2.6.25.) and tried to build it using instructions mentioned on UML kernel  home page. There were no compile or build time errors but while booting the kernel hangs at "VFS:Mounted root(ext3 file system) read only" and prints "runaway loop modprob binfmt-464c" 5-6 imes. I know it's an FAQ but even after digging a lot i couldn't find a reasonable solution.I also couldn't find how to disable CONFIG_COMPAT_VDSO on my ubuntu.
I'm curious to know y did it work previously and not after building from source?
Some other details of my env:-
1) Host Ubuntu 9.04 64 bit kernel
2) UML 32 bit kernel 2.6.25
3) File system used with UML is fedora10_x86_root fs.

Any help is greatly appreciated.