converting videos

Viewty LG990i I cannot solve the following problem. I have a spanish video course, format FLV. I have converted them to mp4 to play on my 990i. All the files will convert and do appear on the 2gb sd card, however, converted videos of around 10mb/3 minutes will play. Anything bigger does not appear on the sd card when inserted into the phone although the files are on the card and can be played on my PC. Any ideas re a solution.