It won't load? So like, when you type it, nothing happens, or the game crashes?
Did you put it in a pre-made group? Like MyRocks, Default, MyTrees, etc? Or your own group?
Custom objects. Everyone thinks they are easy, but aren't actually. You need mesh making programs, and I recommend Blender. It may be somewhat hard to find, but I think you can find it on ogreblender.org (or something like that. xD)