If that error appeared when you started the download, that could be because you clicked Open rather than Save. Buyers must Save the full download to their computer before they can then Open the complete file in their media player.
If the error appeared after downloading when you attempted to open the finished download file, the problem may be with your Remote Product File URL. Our system takes everything after the last "/" in the URL to be the filename for the download, so your computer may not understand how to open a file named "6156b09e.mp4_expires=1504803262_awsaccesskeyid+akiajajz4wcfn2dr4rgq_si gnature=b033p9kaynbv4pt4a6jzuy", rather than just "6156b09e.mp4". It also appears that file URL will eventually expire, so you'd probably need to edit the product's settings periodically to update those URLs after they expire, which could become a hassle.
Using a third-party video hosting service which is merely storing your video files on Amazon S3 and serving them to us from there is probably overkill for our purposes and likely contributing to the filename complications above. You don't really need any specialized "video hosting" service to store video files for us to deliver to your buyers, so any generic file hosting server would suffice. The fact that file happens to contain video content is irrelevant to our system, and we never expose the full, original remote file URL to your buyers.
It would be simpler and probably also cheaper to cut out that video hosting middleman and just store your .mp4 video files directly on Amazon S3 yourself. Just set your files to be Public and obtain the public link URL for each file -- note that "public" does not mean your files would be listed or exposed anywhere for the general public to discover; it just means anyone who already knows the exact URL for the file can access it at that URL without any further restrictions, similar to having an unlisted phone number. The unique download links we issue to each buyer will cloak your remote file URLs and enforce your link expiration settings.