When I had the exact same problem ages ago, it was because the Apache mod_so wasn't enabled.
Run your Apache binary with the -l option, which will list all of the modules complied into Apache.
If mod_so isn;t installed, try recompiling Apache with mod_so support (see Apache's README.configure) for instructions, if you need them.
If mod_so is installed, I can't help you - that was the cuase of the problem for me.