Recompile kernel with no 4GB support

Hello list, I was trying to recompile the stardard kernel source that comes with 7.3 (aka 2.4.10). When I try to switch off the kernel support for 4GB (that I do not need in a 128Mb laptop) I am no longer able to boot this kernel. The system hangs at boot time with a kernel panic message: unable to mount fs. By the way I use Reiserfs in my root partition and I do create init images with mk_initrd for loading this module at boot time. It works fine... until I switch off 4GB support. Does it concern the file system? Why it isn't able to mount the fs without 4GB support? Is this something weird or I do miss something important?