That's not what happened to me, but maybe my solution will help you too. Maybe you changed your Steemit password? If so, try logging in and out of DTube with the new credentials, via SteemConnect. Because it could be the case, that you are still logged into DTube with the old password.
If not, maybe try another browser, check if the file name is not in capital letters (e. g. *.MP4). Also make sure you upload the Snap, WHILE the video is uploading.

I also wrote about an error here: https://steemit.com/dtube/@trustert/fix-dtube-error-while-submitting-to-the-blockchain