This is mainly caused due to activation issue with Adobe Digital Editions.
Please connect your eBook Reader with your PC/Mac.With device connected and showing in ADE hit Ctrl-Shift-E (Cmd-Shift-E on the Mac). This should bring up the deactivate device dialog - use it to deactivate your device.
Quit ADE, and relaunch ADE (with your eBook device still attached), and you should get a device activation dialog, Activate it and then copy.
Have you digital Edition and reader authorize with the same adobe id?
Thanks I've kept this in case I get another problem. I went back to the book site and found in their FAQ that I needed to authorise with an ID which I hadn't originally. So I reauthorized. It took several attempts to then copy to ereader because it wouldn't recognise the Adobe ID I had - ended up using 3 different email addresses with new Adobe ID for each before it would finally accept one for me to copy to ereader. Hope I don't have this trouble again because I'll have too many email addresses to remember!
Thank you, I got there in the end-took me about 2 hours! Thought technology was meant to make life simpler but I'm not that good at it unfortunately.
You are welcome.
It wont let me "Cmd+Shift+E" on my digital edition. Is there any other way to deactivate my device?