If you client was ok last week but you have tried to
log in after Tuesday March 01 and cannot it's a very
simple fix, thanks to SaintBolomas.

Download http://www.gamefront.com/files/20053363/TOwowCN3.3.5.13685.rar

This is a new version of an old file used before, with the new updates.

Put this folder into your wow directory.

Run the bat file, select incremental update.

Your fixed.

The other post is a bit confusing, It's not Thursday either.