i also update from 5.0.5 and same problem, 3 wow friend had same client as i they updated with no problem.
this was yesterday when i first made my account.
this morning i run pandawow.exe and i was enable to login i lvl a toon to lvl 4 had to log off, when i came back i had the same error agian that NamelessIdiot had agian.
i did all steps now reboot modem/router chance ip, chance password, try other account, try edditing files, deleting cashe.
i download the whole game true battle.net and put pandawow.exe and wtf file in it and the error chanced.
Its now saying "This account needs to be converted to a battle.net account"
non of the options i looked for on forum helpt.
help