I am unable to open my purchased ADE books in Digital Editions.

I have been able to open and read my purchased ebooks in Digital Editions in the past but now when I try to open them I get  get the following error message.

"There was an error opening this document. The security plug-in required by this command is unavailable."

Could this be due to the fact that I have installed some updates in my OS ? I am not sure what to do to reinstate my books.

I would appreciate any suggestions.

Many thanks.