Please check the below to the files are compatible with COWON M2.

* Supported File Formats - AVI, WMV, ASF
* Supported Video Codecss - XviD SP/ASP, WMV 7/8/9
(screen resolution, frame rate, bit rate, and other options may affect
the playback of some clips)
* Video Resolution - 320x240, 30fps (recommended)
* Audio Codecs - MPEG1/2/2.5 Layer 3, WMA
* Subtitle - SMI

Please check the file information with COWON Media Center- JetAudio. If your file is not playing on COWON M2 even though your file is encoded with those specifications, your file might be damaged. Please convert the file again by using COWON Media Center, JetAudio for use in COWON M2.