'class_initializer.php' issues!

[Kyttias]

If error reporting has been turned off in php.ini, the "notices" should not be occurring. Temporarily shut off MAMP, or restart your computer if you don't know how, and turn it back on. Major changes won't go through until the server has been restarted.

As for that particular fatal error, I've only seen that happen when the default theme is changed incorrectly. Did you change the default theme name during installation?

Other people with this error: [ x ], [ x ], [ x ], [ x ]

There is also an off chance your config.php is not filled with the correct information, or that the correct information was not entered during installation.