Burning Crusade Classic Patch Notes Version 2.5.4

[Flinda-sulfuras]

What's with this error message?

BNet will not launch the game. Here’s the error that is reported: An updated version of World of Warcraft is available. Please launch the Battle.net app to download the update. However, this error is delivered in a text window, not a Blizzard Error Message. Classic launches just fine. Retail? Nope. Can anyone explain what’s going on and what I need to do to the game to launch?

Will fix this issue. It did for me.