Download Button is Greyed Out.

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

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.