Huhm, it's weird seeing how nothing is printed out, since the class is working fine on my site (cant post link here since it's on localhost)

I just wonder why it doesnt print out any error though, weird, lol

Just to test, try putting this right below the <?php in the simple category class file:
die("blah");
I just wonder if the file is even read and executed, that's all.
If you see blah appears on the site, then you know it's read and excuted. Then you can cut that line and paste it somewhere below that, probably in the init function, and so on and so forth to see where the code stops executing.

Normally, turning on strict error report will point out where the error is right away, i dont know why it doesnt work here though.