From 12:11PM to 2:26 PM (GMT+9), players experienced difficulties entering the game on steam due to an issue with Steam identification process. 
It has been identified as a Steam server-related issue, and everything is now back to normal. 
As a compensation reward, all players connecting to the game within today will receive 5,000 Gold though their in-game mailbox. 
Sorry for the inconvenience you may have encountered.