Apple customers using iWork ‘09, have reported that, in some rare cases, the serial number prompt won’t go away, even after installing the full version of the software.

The company informs that, although installing the full version of iWork should allow customers to start using Pages, Keynote and Numbers without problems, in some cases the installation process may be blocked by a dialog asking the user to input their serial number.

This may happen if a trial version of iWork ’09 is already installed and it is a higher version number than the one being installed from DVD.

The resolution is fairly simple. Basically users need to delete a couple of files. However, not everyone will know where to locate them.

The proper procedure, as outlined by Apple themselves, is:

1. In the Finder, click the Go menu and choose Applications.
2. Locate the “iWork ’09″ folder and drag it to the Trash.
3. Click the Go menu once again and and choose Go to Folder.
4. In the prompt, type:  /Library
5. Click the Go button.
6. Open the Application Support folder.
7. Locate the “iWork ’09″ folder and drag it to the Trash.
8. Return to /Library using the back arrow in the Finder window.
9. Open the Preferences folder.
10. Locate the files “com.apple.iWork09.plist” and “com.apple.iWork09.Installer.plist” and drag these to the trash.
11. Reinstall iWork from your Installation DVD.