This error occurs when your computer does not realize which program is necessary to use the book file. Before proceeding, please make sure you have fully installed Adobe Digital Editions! Below is how to fix this based on the version of Windows your computer has: Windows 8: Associate a File Type to Adobe Digital Editions
1. Open your right-side menu, and select Settings then Control Panel.
2. Go to Programs, Default Programs, and select "Make a file type always open in a specific program."
3. Find .acsm in the file extensions list. Click it one time to select it.
4. Click the "Change program" button above the list.
5. An "Open with" box will come up. Select Adobe Digital Editions from the list of programs recommended.
6. Click OK. Your ebooks should now default to opening in Adobe Digital Editions.
Windows Vista or 7: Associate File Type to Adobe Digital Editions
1. On your computer, go to Start, then Control Panel.
2. Select Programs, then Default Programs.
3. Open "Associate a file type or protocol with a program." This window may take a minute to load, it contains a lot of information.
4. Find .acsm in the file extensions list. Click it one time to select it.
5. Click the "Change program" button above the list.
6. An "Open with" box will come up. Select Adobe Digital Editions from the list of programs recommended. Note: if ADE is not listed, please double-check that it is installed on your computer, or use the "Browse" button to find and select it.
7. Click OK. Your ebooks should now default to opening in Adobe Digital Editions.
Windows XP: Associate File Type to Adobe Digital Editions
1. Open 'My Computer' and select Tools menu > Folder Options. The 'Folder Options' dialog box is displayed.
2. Select the 'File Types' tab. A list of all file types will be displayed--this may take a minute to fully generate.
3. Select '.acsm' in the file extentions list and click the 'Change' button.
4. Select 'Adobe Digital Editions' and click 'OK'. Adobe Digital Editions is now set to open ACSM files.
Mac Computers:
1. In Finder, select the Downloads folder.
2. Scroll down and find the .acsm file (this was the attempted book download).
3. Hold down the Control key, and click on the .acsm file.
4. This opens a small menu - choose "Always open with..." and set to Adobe Digital Editions.
Older Macs - if "always open with" is not an option - start as above then:
4. Select "Open" then "Other."
5. A new window opens. Select Adobe Digital Editions from the list and check the "Always open with" box.