Your Clip+ might be set to Auto Defect USB mode, in which case it might connect to your Mac in MSC mode, and possibly in MTP mode when you plugged it into the Windows machine. It will do this if it detects Windows Media Player. Files put on in one mode are not visible or accessible while connected in the other.
Try manualy setting it to MSC in Settings > System Settings > USB Mode and see if they show up now on the Windows machine.
Your Clip+ might be set to Auto Defect USB mode, in which case it might connect to your Mac in MSC mode, and possibly in MTP mode when you plugged it into the Windows machine. It will do this if it detects Windows Media Player. Files put on in one mode are not visible or accessible while connected in the other.
Try manually setting it to MSC in Settings > System Settings > USB Mode and see if they show up now on the Windows machine.
My Sansa Clip+ has been soaked and i cant turn it back on and ive had it since December 2009