I tried logging in today and had the same issue, let me tell you how I fixed it.
http://www.mygame.in.th/movement/notice_20121108_1.asp?option=Mstar
1. Click the orange button.
2. Log into your account
3. Fill in your old password, and then a new password.
I guess for security reasons they want us to update our password, but yeah that's all.