Unsupported Resolution?

I tried to put a video into my Samsung Gravity T669 and when I tried to play it on my phone it says “Unsupported resolution”. I randomly took a video and saved it, the resolution of the video i took was 320 x 240, mp4 file. So I converted the video I wanted to a mp4 file and made sure the resolution was 320 x 240 but it still says unsupported resolution. If anyone has this same problem or know how to solve it please answer asap. Thank you.