This error means that the Battle.net Update Agent couldn't open files to initiate streaming. Streaming is the method we use to install and update our games. It allows you to play before the installation or patch is completely finished. If you choose to play before the game is completely installed or patched, the stream will continue to download missing data while you play.
If the issue persists, please allow the Battle.net Update Agent fully download game data prior to pressing Play.
Tried everything here?
If you have tried all of the steps for your operating system and still require assistance, visit our Technical Support Forum (World of Warcraft) (StarCraft II) (Diablo III) (Hearthstone) or contact us.
Article ID: 6645