
This article describes required Windows setting for succesful parameter conversion MR-J2S-A -> MR-J4-A
In MR Configurator2 "Parameter converter" tool can display error that parameter file cannot be opened:
When parameters file that you're trying to convert contains parameters with decimal parts, converter can't correctly read those parameters when you have default decimal separator set in Windows as comma ",".
You can check if parameters file contains parameters like this in notepad:
34 Ratio of load
inertia moment 15.8 times 0.0-300.0
61 Ratio of load
inertia moment27.0 times 0.0-300.0
Changing default decimal separator in Windows to dot "." will allow you to succesfully convert parameters:

Remember to relaunch MR Confiurator2 after changing Windows settings