ConnectionOptions oConn = new ConnectionOptions();

oConn.Username = "username";
oConn.Password = "password";
oConn.Authority = "ntlmdomain:XXX";

ManagementScope scope = new ManagementScope("\\Remote_Computer\root\CIMV2", oConn);

scope.Connect();

ObjectQuery query = new ObjectQuery("SELECT DeviceID, VolumeName FROM Win32_LogicalDisk where DeviceID = 'D:'");

ManagementObjectSearcher searcher = new ManagementObjectSearcher(scope, query);

ManagementObjectCollection queryCollection = searcher.Get();

foreach (ManagementObject m in queryCollection)
{
      //error happens here
      fs = m["FreeSpace"].ToString();

      freeSpace = Convert.ToInt64(fs);
}

"SELECT FreeSpace FROM Win32_LogicalDisk where DeviceID = 'D:'"