Sounds like you’re using an outdated solution to build the projects in the OptiX SDK.
The OptiX SDK installation doesn’t contain OBJLoader.cpp/.h anymore after version 3.6.3.
OBJ files are loaded with the OptiXMesh class since 3.7.0, and that also uses the m_accel_desc.
My recommendation would be to de-install and re-install OptiX 3.9.0 to make sure no files have been changed.
Then open CMake at the location “NVIDIA Corporation\OptiX SDK 3.9.0\SDK” and use the CMakelist.txt file there as root to configure and generate the solution containing all examples and sutil.
Press configure and generate to build that new solution.
There should be no complains about missing OBJLoader files at that point.
Then open that newly generated solution and rebuild all.
If that doesn’t work, post the exact errors you see either in CMake or the host compiler along with the usual system information:
OS, installed GPU(s), display driver version, CUDA Toolkit used to compile the PTX code, host compiler version and edition.