mkinitrd failed: it can't find the modules already generated

I'm running Debian of kernel 2.6.8. For study use, I have to compile kernel
2.4.27. After having the kernel image, I used mkinitrd to generate the
initrd.img in this way: "mkinitrd -o /boot/initrd.img-2.4.27 2.4.27".In the
end of the command, I did give the VERSION. But mkinitrd can't find any of
the items I chose to build as module:
: add_modules_dep_2_5: modprobe failed
FATAL: Module floppy.o not found
FATAL: Module ext3.o not found
.........
1.I had succeeded in compiling 2.6.3 to 2.6.8 through the similar approach
with your kind help here:) At that time, there was no such problem.
2.I've succeeded in generating vmlinuz and system.map using "make-kpkg
buildpackage kernel_image, then dpkg -i
kernel-image-2.4.27_10.00.Custom_i386.deb" Should I give make-kpkg some
option like -cramfs?
3.If I don't give mkinitrd the VERSION and use current version by default, I
can have the initrd.img. But kernel 2.4 won't boot using it.
4.I do find floppy.o ext3.o or any other module in /lib/modules/2.4.27/...
It seems that mkinitrd cann't find them. But should I copy so many of them
one by one to the /etc/mkinitrd/modules?
Sincere Appreciation to any advices.