I referred to the following URL on the official website: Adding a Controller — Omniverse IsaacSim latest documentation for writing the controller. The program works fine if the world is not wrapped into a class. However, when I wrap the environment and the robot into a class, the following error occurs.
Isaac Sim 4.1.0 is recommended instead of Isaac Sim 2023.1.1 by Nvidia.
If you would like to use Isaac Sim 2023.1.1, you should refer to old version document.
https://omniverse-content-production.s3-us-west-2.amazonaws.com/Assets/Isaac/Documentation/Isaac-Sim-Docs_2023.1.1/isaacsim/latest/core_api_tutorials/tutorial_core_adding_controller.html
The document shows that Isaac Sim 4.1.0 is changed from Isaac Sim 2023.1.1.
The change may occurs the error.