Classes are loaded like any other files. include_once("path/to/classes/myclacc.inc");
or with require_once(), or just require(). Or you can build the class within the same script page if you choose to.
If the class has a syntax error in it, it will not load with the require() statement, and you will get the 'non-existant class' error.
Try using include_once() to call the file. If it has errors in the class file, it will tell you where the error is. Once you get it working, you can change it back to to require_once().
require() cannot tell you where the error is at within the required file, This is because a file that is required is loaded at run time. An included file is loaded after the initial script is initiated, and the parser can then warn you of the errors.