You could try making sure that you have removed all traces of the old ebook:
.acsm files (probably in your Downloads directory)
.epub files (probably in your Documents/My Digital Editions directory
deleted from Library in ADE
in extremis: edit it out of manifest.xml (probably in your Documents/My Digital Editions directory)
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There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
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