Copied files to Nexus 7 - same size but content zeros

[oceanclub]

I've copied files from my desktop (Windows 7 64-bit) to my Nexus 7 tablet using USB connection. Most work, but occasionally a file wouldn't. When I just checked one now, the bit size is exactly the same as the original but the initial content is simply NULL characters! Anyone know how on earth this might happen and how I should copy files?

P.