In the COMSOL Desktop go to the Preferences and select Security, locate the General section. To permanently enable an external MATLAB function, in the list Allow external MATLAB® functions select Yes. To enable an external MATLAB function only once, set the list Allow external MATLAB® functions to Ask. Using the latter option, you will be asked to enable external functions when the function is run.

In the COMSOL Server™, you need to connect as administrator then go to Administration>Preferences, in the Security section select Allow external MATLAB® functions. Then click Save.

Add the flag -allowexternalmatlab on to the COMSOL startup command to permit external MATLAB functions to run.