PHP Fatal error: Cannot redeclare class

You have a class of the same name declared more than once. Maybe via multiple includes. When including other files you need to use something like

include_once "something.php";

to prevent multiple inclusions. It's very easy for this to happen, though not always obvious, since you could have a long chain of files being included by one another.

It means you've already created a class.

For instance:

class Foo {}

// some code here

class Foo {}

That second Foo would throw the error.