Help Needed with Walkman MP3 Player

Please help! I have purchased a second Walkman MP3 player as my first was lost in a move. I have encountered a problem I cannot solve. My new MP3 player (Walkman NWZ-E384) is refusing to play any music. I have used Windows Media Player, Media One all to no avail. The music is transferring -- I can see the music files when I look at the Walkman contents via my computer. However, when I try to play I continually get the message that I need to download some music. I have no idea where to go from here. I have transferred MP3 files from YouTube and also directly from CDs I own. None of it is being found by the Walkman. I have checked the driver info, and it states it is up to date and is being detected as a MTP USB Device.

Thank you so very much for any help you can provide, it is greatly appreciated!