Got this error also and (local) help-pages stoped working. Not even reinstallation of MATLAB (R2020a, Win 10) helped to resolve the issue.
Seems to be a problem with corrupt preferences. After deleting the preferences directory, and reinstallation, help worked again with no error messages (so far). Type
in the MATLAB command window, exit MATLAB and delete the preferences directory (WARNING! all your custom settings will be lost). I do not think reinstallation is actually necessary after that, just re-starting MATLAB should be sufficent.
After you have set your custom preferences again you might want to exit MATLAB and save a backup copy of the preferences directory so you can replace it if you experience similar problems again.