If you notice your API calls are randomly failing with HRESULT_FROM_WIN32(ERROR_BUSY) / 0x800700AA / -2147024726, then it's likely that the device driver is indeed busy doing something else. It could be that WMP is syncing content to the device, or maybe...

A playlist (.WPL, .M3U, etc.) is a text file which contains a list of filenames. This list is the "playlist". So transferring the playlist should be easy right? Well, yes it is - if you just want to transfer it as a text file... However if you want...