try editing your account details: http://adamantventures.com/blog/adobe-digital-editions-activation-authorization-problems/
you also may be able to resolve the problem by clearing your adobe.com cookie from your browser.
I had a similar problem and this worked for me (the IE assistance came from a helpful person in the forum)
- uninstall ALL versions of Adobe digital editions (I tried v1.7, 2 and 3!)
- use INTERNET EXPLORER to download ADE v 3.
- DISABLE windows firewall BEFORE installing ADE3.
- Install ADE 3 and I found I could then aauthorize my computer using help>authorize computer in the ADE menu.
- Re-download e-book (because previous downloads had expired), and I was able to open my ebook.