Hi again - let me know how things go with v1.6! If it is still a problem, please email me the dmhelper.log file (info@dmhelper.net)
We have tested with several maps from Dynamic Dungeons, which one is causing you grief?
Generally, the video playback uses libvlc from VideoLAN, so if the VLC player is having troubles it is unlikely that the DM Helper will be more successful. And unfortunately that probably means it might be somehow based on a system limitation of your PC. But before we decide that, let's check it out further!