If you want to have your mod load after EVERY other mod, there is an attribute in the @Mod annotation called dependencies. Simply set the attribute equal to the String "afterAll", or specify the mod via "after:Mod".
Did you do TileEntity.addMapping(tileEntityClass, StringId); Or you can use GameRegistry.registerTileEntity(tileEntityClass, StringID); (GameRegistry just uses this TileEntity method anyway, so it doesn't really matter which you use. This caused my tile entity to disappear until I actually mapped it.)
Improper use of the Configuration File Properties caused the ID of one of my blocks to be invalid. This invalid Block ID caused issues with the Rendering and World Generation in Minecraft.