Do ldd /usr/local/aolserver/bin/postgres.so logged in both as a root and as nsadmin. My guess is that when you're logged in as root linker cannot find libpq.so (you'll see this with ldd because the link will be empty). You can fix it by setting LD_LIBRARY_PATH to contain the path to libpq.so or add this path to /etc/ld.so.conf and running ldconfig (as root).
Of course it might be something completely else.
