I often come across this error, it's hard to know exactly what's causing it because we don't get a unique error code. But I will say that taking these steps has solved it for me personally:

1. Log out of DTube
2. Close Browser completely (all tabs and windows)
3. Relaunch Browser
4. Log back into DTube
5. Upload again!

Some other things I've noticed:

• upload your thumbnail while the video is uploading
• don't put too many special characters in the title/description

^ IDK if the two points above affect your error, however I've had very long descriptions with that wouldn't post before and give me that error.