Error! Check Activation

Borrowing a PDF ebook from OpenLibrary, the first time for pdf. (I have borrowed a few epubs from there previously, about a year ago.) Digital Editions is authorized for this computer (only), and from the Help menu, I can display my Adobe ID / Account Number.

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EDITED TO ADD VERSION INFO:

I am running ADE v 2.0.67532. I do not wish to upgrade to v. 3.

The computer is a 32-bit Hewlett-Packard running Windows Vista Business.

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Upon trying to load the acsm file into the Digital Editions library, I get error message "Error! Check Activation" and the book fails to download.  There is no error code provided in the message box.

What do I do to fix this?