That could be happening because you have signed in one too many times with Twitter or Instagram. You must have super-sonic speed! That’s pretty awesome. How about you wait for fifteen minutes before you log in again? That should help.
If that doesn’t work, there’s another way in - log in using any of your other accounts (either Instagram or Twitter).
Once you’ve logged in successfully, go to the Settings of the account that gave you a hard time.
Next, ensure that the box that says “Allow log in using this account” is checked. Your problem should be solved.