Huzuni 1.10 .json file download not saving

Hello my friend has been experiencing issues and I have been trying to help him, we have re-installed minecraft, tried copying every file from my PC to his PC and many more solutions, yes we are trying to fix an add on client, my computer works with it and his doesn't, we even tried turning of his firewall and anti virus. The .json file isn't saving when downloaded and it keeps giving him an error message when it launches.