After many attempts to upload a video to DTube with constant failure, I finally found the solution; so here it is.
First you have to go to Settings on your profile.
Then you must select Wallet and then Permissions.
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After this, you will see your posting key, which will beginning with an "S"
Then select where I have marked with a red pen, and change to hide private key; then copy and save the posting key beginning with a 5. Use THIS password to login to Dtube, and then you can upload your video without an error.