You may have to ReLoad the Ebooks for them to be recognized by the updated version....
Also have you done the update to 9.1.3 yet ??? If Not....
You can do this by Opening the Adobe program and in the toolbar at the top Click the HELP Tab, in the drop down select update and then try again to see if that worked.. If still no success you may have to ReInstall the Older version of Reader as well..This can be Downloaded from the above linked site:
At that site there is a drop down menu at the bottom of the page with all previous versions of Adobe, from 4.0 to Present..
Best of Luck..Hope this Helps..
Another solution.... Open Adobe Reader Program and click on the FILE Tab at the top.
Click on Digital Editions and Install 1.7.1 this should fix your problem with older ebooks not being compatable with version 9