You could have the issue whereby .acsm files do not get properly registered.
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.
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