Download Button is Greyed Out.

Problem:
I have been able to download books successfully and now the Download Button is Greyed out. I am not able to click to Download any book title

Resolution:
The most likely cause of the download button being disabled is due to the user downloading more that 100 book titles in 30 days, 

There is a limit of 100 downloads in 30 days.

The 30 day is a rolling window. Once enough days have passed with no downloads, the total will be less than 100 download in 30 days and the user will be able to download a title once more.