This post is for anyone new to DTube that can't find out how to login to your account. I originally had this problem until I figured it out. A number of people have tried to use their password for https://steemit.com account with their DTube. This is wrong. While your username is the same, your password is not the same.
To find your password for DTube or correctly called private key, here are the directions.
Click on your profile image. From there select Wallet
This will bring you to this
Currently Balances is highlighted. Click on Permissions. That will take you to a page of different passwords. It should give you 4 different passwords that will look something like this.
CLJCqlfxNXkdqISLqdizNVjUGJjALYEPJnsBaxYNWjsntMYlQI
That is a fake password to help you understand what you are looking for.
On the right hand side, you should see this image.
Click on the top "Show Private Key" That will give you a different password under posting. Copy and paste that into your DTube login. That should fix the error you have and let you into your account.