Dawn,
Digital Editions won't 'ask' you to authorize your PRS-505. If the 505 is connected it should just see it, and if the sony library has books then you should be able to open them in ADE 1.5 and read them.
Now, if you have a problem with that same book on the Sony side I'll have to send you to Sony. But if you can open an Adobe web support case and provide some information I can then escalate that over to Sony and they'll get in touch with you. Or maybe it'll be something we can work out here at Adobe. In either situation please open a case...
To open a Digital Editions 1.5 Technical Support case, please use the contact links at http://www.adobe.com/support/digitaleditions.
Regards,
Bentley Wolfe
Senior Support Engineer, Flash/Flash Player/Digital Editions
Adobe