I am now getting the above message when trying to open a .acsm file from my library. I have done this many times before. I now run Windows10. I have installed the latest version of ADE (220.127.116.11394). I tried Adobe online chat but they sent me here! The 'delete key' in the Registry did not work!
OK - sorted!
Found that the version I downloaded 3 days ago was NOT the latest version. Installed v4.5, deleted keys in the Registry, re-authorised and all works fine.