Have you read http://helpx.adobe.com/digital-editions/kb/installing-digital-editions -20-windows.html
It is about installation but give some help on authorization.
Also, may be worth trying v1.7.2; though despite the myriad bugs there are on V2.0, I haven't seen that one come up before.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172