Transfer restrictions when trying to move files from pc to nexus 7

Hello,
I was trying to transfer some mp4 files from my desktop to my nexus 7 when a message popped up stating that it didn't support these types of files.. Something like "it is unable to support these types of files.. Try using windows player to reformat.." Then I have the option of "skip", "skip all" or "cancel". (In the background, it looks like it's slowly copying over). Nehoo.. I've tried selecting all the options but each one just closes out everything! Please help! Thank you in advanced :)

Maybe they have some type of DRM preventing this from happening.

I had same issue with my "ripped-and-backed-up-mp4's" yesterday:

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and installing MX Player solved it. HTH.