Do you get this using one of the media transfer options on the pop-up that shows up when you first plug into Windows? I'm just curious. I never use those options, I just close the dialog box, open windows explorer and have no trouble copying files back and forth from Nexus 5 > Internal Memory > whatever folder and my computer.
I *will* sometimes get a message when I transfer media this way to the Nexus 5 that it might not be usable by the device I am transferring to, do I want to transfer anyway? I always say yes and never have any problems later with playing/viewing the media.