Hi Matadem, yes like Brian says it is likely that you are running different versions of Moi there.

You'll need to update your operating system shell setting to tell it to open MoI v4 when you double click on a .3dm file, currently it is probably opening up MoI v3 when you do that.

You can do that by right clicking on the file and choose "Open with" > "Choose default program" or by other methods as described here:
https://www.lifewire.com/how-to-change-file-associations-in-windows-2624477

- Michael