How to Save video files in MicroSD in LG GX 200 Mobile?

Hi Friends! I am saving some video files in Memory Card (4GB MicroSD) in my LG GX 200 Mobile. But the files are not playing in my mobile and saying "Failed to open the file". I am saving the files in ".3GP" format which supports to play the files in Mobiles. Even, the videos are not playing. Can you please help me. Thank you.