Hello Patrick,
Thank you for the detailed message! I suspect that it is your WordPress is rejecting the file type not our plugin. You probably need to allow the file types in WordPress itself as it does not allow certain file types by default: http://www.wpbeginner.com/wp-tutorials/how-to-add-additional-file-types-to-be-uploaded-in-wordpress/
I'd also try making sure your running php 5.4 or better.
That should fix your issue, if you still have the issue, you might check for conflicts with other plugins or the theme (but I think in this case, it is not likely)
Have a super weekend,
Joseph
VFBPro Support