I compiled pg 7.0.2 with the default block size, and I had the same error as you. I rebuilt the kernel by following the directions. When doing the configuration for the kernel, I just answered yes to any questions regarding ipc and shared memory (I think they were selected as yes for the defaults). After building the kernel, I copied the new kernel to /boot and made it the default kernel using lilo, and after that everything worked fine. cd into /usr/src/linux, and you should find some documention there or somewhere below there for rebuilding your kernel (I don't have a linux machine handy, so I can't check for sure).
