Typical symptoms

You run something like:

• import opensim as osim works, but Moco fails later complaining about CasADi
• import casadi fails with ModuleNotFoundError
• You see DLL load failed, The specified module could not be found, or missing .dll messages
• It works in Anaconda Prompt, but fails in VS Code or PyCharm

Step 1: Confirm you are using the right Conda environment

In Anaconda Prompt:

conda activate opensim_env
where python
python -c "import sys; print(sys.executable)"

Expected: the path points inside your environment, for example:

...\anaconda3\envs\opensim_env\python.exe or ...\Users\<you>\.conda\envs\opensim_env\python.exe

If it points to base, Windows Store Python, or some other Python, you are not in the right interpreter.

Step 2: Check whether CasADi is actually installed in that environment

With opensim_env activated:

conda list casadi
python -c "import casadi; print(casadi.__version__)"

If conda list casadi shows nothing or the import fails, install it:

conda install -c conda-forge casadi

Then test again: