E ADEPT DOCUMENT TYPE UNKNOWN error

I can download a recent book from google play, but when I try and open it using Digital editions so I can read it I keep getting ' e adept document type unknown' error. Am using ADE 4.5 (just updated).

Have tried deactivating and reactivating Adobe ID and still doesn't work.

Have tried completely removing ADE from my PC (using registry etc) and nothing.

Have tried deleting and redownloading the book a million times and it doesn't help.

Have tried adjusting system date and time, and guess what? It doesn't help.

Google say they can't help, and Adobe just refer me to these forums where I see that this question has been asked again and again since 2014 with no assistance.

Please help.