Hello, I start to have this problem after install the new version de blender, before all was working well.
I try exporting even a simple cube only and it give me the same message. So I guess the problem is not the file.. its something from the configuration or something…
I'm using win10 64
((when I open first time the version 2.78 blender I update the user file from the previous))
((Later I back to make a new installation clean without the previous user file.. and I had the same result)