Exporting problem

Hi, am using a trial version of toon boom harmony advance 15 and first exporting for test video worked using VLC player but when i created new scense and export with same steps the video is not playing, it only play if i convert the video to different extension
So the question is, is this because of limitations of trial version or i missed some thing?

Note: when am trying to make changes in the first scense file and export again it is playing well. But any new exporting for new scense is not played.
Any suggestions?