Be sure to make all the recommended changes to your Windows (XP, Vista or Win7). Some relate to videos.
Are your video files on an external drive or an internal holding Windows? Again, there are some Windows changes we recommend that allow video files to play from external drives.
Be sure to check the Hoster upgrades page at
http://www.mtu.com/upgrades/hoster#Upgrades. As a beta tester, you should be running the latest 4.32.10 version.
