MDL material path failed

Omniverse Isaac Sim
1

I encounted error when I created a materials (OmniSurface)

Ubuntu: 22.04
GPU: A6000

IsaacSim: 4.5.1
IsaacLab: 2.1.0
IsaacSim installed by pip (using conda environment) ( I followed Installation using Isaac Sim pip — Isaac Lab Documentation )

After I created a materials in World:
2025-12-03 10:16:36 [33,666ms] [Error] [rtx.neuraylib.plugin] [MDLC:COMPILER] 1.0 MDLC comp error: C120 could not find module ‘::Z73file_3A::home::Z99vmo_2Ddell3680::anaconda3::envs::env_isaaclab::lib::Z0Cpython3_2E10::ZC9site_2Dpackages::omni::mdl::core::Base::OmniSurface’ in module path
2025-12-03 10:16:36 [33,666ms] [Warning] [rtx.neuraylib.plugin] Loading MdlModule to DB (rtx_scope0) failed: ::Z73file_3A::home::Z99vmo_2Ddell3680::anaconda3::envs::env_isaaclab::lib::Z0Cpython3_2E10::ZC9site_2Dpackages::omni::mdl::core::Base::OmniSurface
2025-12-03 10:16:36 [33,666ms] [Warning] [rtx.neuraylib.plugin] Loading transaction committed (this thread). MdlModule is NOT in the DB (rtx_scope0): ::Z73file_3A::home::Z99vmo_2Ddell3680::anaconda3::envs::env_isaaclab::lib::Z0Cpython3_2E10::ZC9site_2Dpackages::omni::mdl::core::Base::OmniSurface
2025-12-03 10:16:36 [33,673ms] [Warning] [omni.kit.material.library.material_library] process_ov_neuraylib: failed to get module from /home/nta/anaconda3/envs/env_isaaclab/lib/python3.10/site-packages/omni/mdl/core/Base/OmniSurface.mdl
2025-12-03 10:16:36 [33,725ms] [Warning] [rtx.neuraylib.plugin] Loading MdlModule to DB (OmniUsdMdl) failed: ::
2025-12-03 10:16:36 [33,725ms] [Warning] [rtx.neuraylib.plugin] Loading transaction committed (this thread). MdlModule is NOT in the DB (OmniUsdMdl): ::
2025-12-03 10:16:36 [33,727ms] [Error] [asyncio] Task exception was never retrieved
future: <Task finished name=‘Task-183’ coro=<UsdShadeBaseWidget.load_mdl_modules..load_module() done, defined at /home/nta/miniconda3/envs/env_isaaclab/lib/python3.10/site-packages/isaacsim/extscache/omni.kit.property.material-1.10.17+d02c707b/omni/kit/property/material/scripts/widgets/usdshade/base_widget.py:336> exception=ErrorException(Error in 'pxrInternal_v0_22__pxrReserved_::Neuray::LoadModule’ at line 242 in file ../../source/plugins/omni.usdMdl/neuray.cpp : ‘‘rtx::neuraylib::MdlModuleId’ for ‘’ is Invalid’)>
Traceback (most recent call last):
File “/home/nta/miniconda3/envs/env_isaaclab/lib/python3.10/site-packages/isaacsim/extscache/omni.kit.property.material-1.10.17+d02c707b/omni/kit/property/material/scripts/widgets/usdshade/base_widget.py”, line 337, in load_module
UsdMdl.RegistryUtils.AddModuleToRegistry(source_asset)
pxr.Tf.ErrorException:
Error in ‘pxrInternal_v0_22__pxrReserved__::Neuray::LoadModule’ at line 242 in file ../../source/plugins/omni.usdMdl/neuray.cpp : ‘‘rtx::neuraylib::MdlModuleId’ for ‘’ is Invalid’

How to fix it??
Thanks.

3

Hi apologies for the delay. Have you gotten past this issue yet, or is it still blocking you?

4

This usually means the OmniSurface MDL file is not installed or not on the MDL search path.

– In your env_isaaclab, check that …/site-packages/omni/mdl/core/Base/OmniSurface.mdl actually exists. If not, reinstall Isaac Sim via the official pip steps for 4.5.1, including the extensions/extscache package.

– In Isaac Sim settings, add …/site-packages/omni/mdl to the MDL search paths if it is missing, then restart.

– If it still fails, try clearing Omniverse user data (~/.nvidia-omniverse or ~/.local/share/ov, path can vary), restart Isaac Sim, and test again.