Never seen an error like this one launching WoW. I’m getting a little popup that says:
“The CAS system was unable to initialize: Tact instance creation failed.
Error (16): container locked
Tact instance creation failed. Error (16)” container locked"
This is right after the update finished. I’ve quit Bnet and restarted and that didn’t help anything. Very strange.
Google says to remove the Read Only flag on your WoW installation folder.
Give it a try I guess, but I’ve never experienced it.
This is what happens when you don’t regularly lubricate the fleagle florp.
/moo 
I can’t even find that, unless it means the entire WoW folder itself?
Yeah.
Program Files → Right click the WoW folder → Properties → Read-only
Seems to have worked. Thanks! Wonder why the update marked it read only. I know I didn’t do it.
pause all other game version updates, classic, etc… and try again, worked for me the other day
I had this problem, i just restarted my pc and it fixed it.
I just got this today. Worked fine yesterday.
Try being a little less crude when you fire up the game.
The only time I get that is when my internet has gone off for a short bit, personally.
I think it has to do with the beta download, I ran into the same issue today while allowing it to download for a bit and then tried to launch the game. Once the download paused it seemed to unlock itself again.
every time i start wow or it gets patched, the folder goes back to read only and get the error again
All the different versions of WoW like classic, or cataclysm, or even possibly retail seem to share certain global files. Maybe related to the graphics engine? But I can’t say for sure. What it does do is lock all the WoW versions while it downloads any and all WoW updates until they’re done.
To make it worse the Blizzard app only shows updating for which ever classic version you have selected in the launch field. For example it was updating vanilla classic and locked the files. But my launcher was set to cata classic and until I actually checked every version I had no idea why my game was locked. If the one you want to play is up to date, just check all the rest, pause them, and you should be ready to rock.
No its definitely the muffler bearings
Worked for me. Much appreciated!
Galeradon is right on this, removed the tick from read only and it worked, new to me nothing ever works the first time, think im figuring out why i get kicked from lfr a lot lol
Thanks! I just got this error trying to launch retail, after updating classic. Your solution worked 
I remove the tick from read only in attributes and for some reason it just keeps turning back on. Makes me love troubleshooting computer issues even more When none of it makes sense