Hey, slow down cowboy. In case you hadn't noticed, I was trying to help. No good deed goes unpunished, I suppose.
Anyway, your subject line says "rewriterules not working with custom php cgi/ini", which is about four words too long. There seems to be a lot of confusion around here as to the exact relationship between PHP and Apache directives (including, but not limited to, mod_rewrite), so I wanted to clear that up first.
You guessed that the answer would lie in your error log, which puts you ahead of the game as far as most new posters here go, so that was actually a compliment. But you can read that line as "as you know" instead of "as you've guessed" if it makes you feel better.
Finally, with the exception of the part where you asked about the location of the error log, your post wasn't very clearly written. Perhaps you could benefit from learning to ask better questions. Perhaps you should also try not to insult people who are trying to help you with your configuration problems.
If you want useful replies, ask smart questions.