I ran into an issue recently where I tried to copy a battle.net game (Heroes of the Storm) from a backup folder on my NAS onto a new computer. Once the copy was completed I couldn’t get battle.net to update the game. It kept failing with error code:

BLZBNTAGT00000840

file update failed for an unknown reason.

After much digging I found this post which mentions it’s due to the fact that the updater apparertly can’t update files with the hidden attribute. The hidden file attribute gets applied by the NAS because the file in question has a dot in front of it in the filename. For some reason the updater can’t touch it.

The fix is to change all files in the game folder to not have the hidden attribute. The easiest way to do this is via the command line. Navigate to the folder of the game you copied over and execute the following:

attrib -H .* /S

Finally, I can copy Blizzard game backups without agonizing over why they won’t patch.