E_ACT_TOO_MANY_ACTIVATIONS

I can't open my ebook in my Android mobile and get the message 'E_ACT_TOO_MANY_ACTIVATIONS'. I only authorize two of my devices, one of them is my pc, another is my Android mobile. For my pc , I can read the ebook all the time. But it always require me to authorize when I use my Android mobile to read the ebook. What should I do?