You could have the issue whereby .acsm files do not get properly registered.
See http://forums.adobe.com/thread/1213041?tstart=0
One solution to may issues with ADE2.0 is to use the more reliable v1.7.2,
Try that and see if it helps.
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
