Digital editions

I have just purchased a KOBO e reader and as instructed on Play.com website downloaded digital editions to transfer books from my library. Unfortunately when I try transfer the books it says I don't have permission. Also the KOBO reader is not authorised which I think is the problem . The option to authorise the device is there, but it is greyed out and will not function. Any ideas how to activate the authorise button, gratefully received. Thanks

Update..... I closed and re opened digital editions and now the option to authorise is available but it now lists ADOBE as the e book vendor and wont allow me to change it to PLAY.COM. it is greyed. so still stuck ..........