Hi,
are you able to browse all the folders in the Mezzmo application on your PC to see the files? The problem could be just limited to when browsing on the device, if you try to browse into an unreachable folder does it error or just not appear in the list?

For the avi files it depends upon the device profile as to whether the files will be transcoded, can you please tell us the device profile you currently have configured for the device in 'Media Devices'?