launcing a .launch.py file in ros2 error

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i wanna run a launch file to open my simulated robot in gazebo and rviz, it worked previously but when i downloaded slamtoolbox and also restarted the cpu, it cannot run anymore. I have checked the xml files and xacro files. Here is the error snippet i obtained:

nvidia@nvidia-desktop:~/dev_ws/src$ ros2 launch my_bot launch_sim.launch.py Task exception was never retrieved future: <task finished="" name="Task-2" coro="&lt;LaunchService._process_one_event()" done,="" defined="" at="" opt="" ros="" foxy="" lib="" python3.8="" site-packages="" launch="" launch_service.py:226=""> exception=ExpatError('mismatched tag: line 40, column 3')> Traceback (most recent call last): File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 228, in _process_one_event await self.__process_event(next_event) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 248, in __process_event visit_all_entities_and_collect_futures(entity, self.__context)) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context) [Previous line repeated 1 more time] File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 38, in visit_all_entities_and_collect_futures sub_entities = entity.visit(context) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/action.py", line 108, in visit return self.execute(context) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/actions/include_launch_description.py", line 130, in execute launch_description = self.__launch_description_source.get_launch_description(context) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_source.py", line 84, in get_launch_description self._get_launch_description(self.__expanded_location) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/python_launch_description_source.py", line 51, in _get_launch_description return get_launch_description_from_python_launch_file(location) File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/python_launch_file_utilities.py", line 68, in get_launch_description_from_python_launch_file return getattr(launch_file_module, 'generate_launch_description')() File "/home/nvidia/dev_ws/src/install/my_bot/share/my_bot/launch/rsp.launch.py", line 21, in generate_launch_description robot_description_config = xacro.process_file(xacro_file) File "/opt/ros/foxy/lib/python3.8/site-packages/xacro/__init__.py", line 1074, in process_file process_doc(doc, **kwargs) File "/opt/ros/foxy/lib/python3.8/site-packages/xacro/__init__.py", line 1025, in process_doc eval_all(doc.documentElement, macros, symbols) File "/opt/ros/foxy/lib/python3.8/site-packages/xacro/__init__.py", line 905, in eval_all process_include(node, macros, symbols, eval_all) File "/opt/ros/foxy/lib/python3.8/site-packages/xacro/__init__.py", line 502, in process_include include = parse(None, filename).documentElement File "/opt/ros/foxy/lib/python3.8/site-packages/xacro/__init__.py", line 994, in parse return xml.dom.minidom.parse(inp) File "/usr/lib/python3.8/xml/dom/minidom.py", line 1959, in parse return expatbuilder.parse(file) File "/usr/lib/python3.8/xml/dom/expatbuilder.py", line 913, in parse result = builder.parseFile(file) File "/usr/lib/python3.8/xml/dom/expatbuilder.py", line 207, in parseFile parser.Parse(buffer, 0) xml.parsers.expat.ExpatError: mismatched tag ... (more)