problem with kernel modules

Hello,
I compiled my own custom kernel image and then I built a new
base-image which includes that kernel. When I run my image, depmod
gives a list of "WARNING: Couldn't find symtab and strtab in module"
and, when I try to modprobe any module, I get a "modprobe: Failed to
load module ***: invalid module format." error.
All images have been generated using openembedded/bitbake, thus the
kernel modules should be automatically generated accordingly to the
compiled kernel image, isn't it?? So I cannot understand this mismatch
between kernel and modules format...
Any Idea would very appreciated! Please help!

Thanks.

Daniele