I'm having the same problem, also using a macbook and os 10.4.6. It occured after one of two things - probably the second...
1. I installe x-code. I don't think this is the problem, but I hadn't checked apache since I did this.
2. I tried to build php4.3 (i am new to working with unix in this way, and have never built/compiled - only used binaries.) It wasn't working out, so I tried to undo what I did by removing the files I had installed. This also involved installing and using fink, and installing some libraries, which I probably should have read more about before I did. I was trying to follow instructions, but I must have done something wrong.
I have already replaced the httpd.conf with the httpd.bak. This did not help.
The message I am getting in the console is:
Processing config directory: /private/etc/httpd/users/*.conf
Processing config file: /private/etc/httpd/users/+entropy-php.conf
fopen: No such file or directory
httpd: could not open
but that is not true because that path and those files do exist.
Any advice or suggestions would be appreciated. Thanks.