What's this error msg i'm getting?

Fatal error: Cannot run code from this file in conjunction with non encoded files in

Is it due to Zend Encoder? I have it enabled.

What's causing it?

When does it happen?

In my MVC's index.php controller

You are including a Zend encoded file somewhere, I believe Zend Encoder does have a feature that will not allow you to include it in files that are not encoded (to prevent someone from using the Reflector object to dissasemble the code).