Mp3 files are supported by Sansa ClipJam however there might be some attributes associated with it that might be causing the issue. You can check the supported file type and attributes supported by Sansa ClipJam :http://kb.sandisk.com/app/answers/detail/a_id/14130. Also, you can contact SanDisk Support at 866-726-3475 and provide them with the Sample File, so that they can check and isolate the root cause for you.