I had the same issue today, after using Ampps on Mountain Lion for weeks with no problems. I knew it must a configuration issue, but I couldn't get to the bottom of it. I tried everything I could think of, including the steps that tidus recommended.
No idea why, but the only thing that worked for me was manually setting the PHP version to 5.2. I'm guessing my config for PHP 5.3 is still messed up, but I'll worry about that later