knowing the format and codecs will be helpful if you can provide that info.
as far as moving the file to vlc, that requires copying the video to the internal memory of your iOS device. how much free space do you have on your iOS device.
If you can upload one of the trouble files to dropbox or something like that you can PM me with a link to the file and I will take a look and see if I can find the issue with the file.
