Hey there friends,
What Deathstar699 said hit’s the nail on the head. This most of the time is just the keys not being on the account or not being valid for some reason. To be clear, you only need a Reign of Chaos or Warcraft 3 Reforged key on your account to log in. We have talked a bit about this in other threads.
Please feel free to post back or reach out to support for more help!
/Nathardrick