This sounds a little like the problem arising when a user account has been affected by the Rogue Glitch... this tends to cause the website not recognizing your username/password combination.
Have you been able to login through a computer or via mobile phone without this problem? If so, please check your account edit page and see if all data is mentioned there correctly, specifically your email address and password.
If these are both correct and you are able to login with a computer normally, I would advise you to contact Ferret (AG admin: ferret@armorgames.com) and explain it to him. He can help you to try and fix this, ok? =)