GetDetailsOf is not working on server

Folder fldr = shl.NameSpace(@"C:\App\Documents");
FolderItem itm = fldr.ParseName("2812122a6f-be0f-4eb0-a82a-8c2daa541233.xlsx");
for (int i = 0; i < 100; i++)
{
    string propValue = fldr.GetDetailsOf(itm, i);
    outputfile.WriteLine(propValue);
    outputfile.WriteLine(fldr.GetDetailsOf(null, i));

    if (propValue != "" && fldr.GetDetailsOf(null, i)=="Comments")
    {
        Comments  = propValue;
    }
}