Hi naxos, I've added a new script method for the next v3 beta so that this will be able to work in v3.
With the next beta you'll be able to use this for the ConvertFolder() function inside the Convert.js file:

    function ConvertFolder( FolderName, FileExtensionToLoad )
    {
        // Convert all files within a given folder, that have the given file extension.
        // For example, convert all .3dm files inside of the folder c:\test :
        // ConvertFolder( 'c:\\test', '3dm' );
    
        var Files = moi.filesystem.getFiles( FolderName, '*.' + FileExtensionToLoad );
   
        for ( var i = 0; i < Files.length; ++i )
            Convert( Files.item(i) );
    }

But until the next v3 beta is out you'll need to use that version you've already got but with MoI version 2 instead of MoI version 3.

Thanks for reporting the problem so I could get v3 tuned up.

- Michael