My ebook reader is saying "file open failed" why?

I bought the ebook through waterstones, via ADE and transferred it to my ebook but can't open the file.

I noticed ADE is authorised to my old email and I bought the ebook via my new email, is this an issue?

How do I get ADE authorised to my new email? I changed the email at adobe.com account.

Now I can't even see the device in ADE when I connect it to my windows laptop!