Q: My username can't be used to unlock this iphone

Yesterday I installed the lasted ios9 update on my iphone. Today, while using my iPhone, I suddenly received an activate your iphone prompt. Unfortunately, I could no longer remember my password, so I had no choice but to reset my apple ID's password. After having reset it, I tried to activate my iPhone using the new password. However, I am now getting a message which says "(my iphone ID) cannot be used to unlock this Iphone. This is exactly the same username I used for resetting my password. I am pretty sure it is the correct one. I would appreciate some suggestions, thanks.