There can be many reasons why you can’t login to an account. Every time you try without success you will receive an error message hinting what the issue might be.
· ""The Username or Password Entered does not Exist""
· ""You are already logged in""
· ""Establishing Connection to the Server""
· ""Your Account has been Temporarily Disabled""
· ""Due to recent version updates we kindly ask our Play Money players to re-register""
· ""Our services may no longer be offered to your country of residence""
All these messages are self-explanatory and they actually tell you what the problem is. If the problem persists then you should contact Customer Support and they will look into the issue.