module insertion

hi
i compiled a hello module in linux-2.6.27.9 (not the running kernel) and i tried to insert it to the running kernel 2.6.15 .then i am getting the following error.

insmod: error inserting './hello.ko': -1 Invalid module format

so is this is not possible to compile the module in one version of linux and and run on another ?

thanks in advance

Can U post ur Makefile ??