The problem may be the path so double check it but...
the problem may be the loop object statement. If the object you are loading doesn't have animation data in it then any play object/loop object statements don't apply, it's just a static object. You said it was your own x model object. If you created it then you should know if it has animation. If you didn't create it, then it is most likely the problem that you are substituting a static object for one that had animations-and that's what the code expects. To test your x model make a new project, load the object then add a PLAY OBJECT num statement and run it. does it blow up? then it's the object not having anim data.
I suggest you start slow and easy with dbp. Although what you did is very proactive, blindly substituting models in code that wasn't written for them will undoubtedly get you trouble sooner or later.
-RUST-