MacFixIt reader "Neil" wrote in, mentioning he had fixed this issue by tackling the preference files associated with the viewer. There are three files, all of which are located in the /username/Library/Preferences/ folder:
As with resetting any settings file for applications, removing these files may clear up a number of miscellaneous problems, including incorrect content being displayed, the help viewer window being displayed in odd places, and the help viewer being blank. After clearing these preference files you should be able to start up the viewer from any application that supports it; however, if the problem still persists then try logging out and logging back in after the files have been removed.
Many help files that load in the help viewer are located in the /Macintosh HD/Library/Documentation/ folder. Being a globally accessible location, the system keeps a record for what the permissions of this folder should be, and applications that install help documentation to this folder may also install a receipt file that the system can use to ensure permissions for the help files are as they were intended by the developer.
Because of this, you can use the system's Permissions Repair routine to ensure files in the global library are properly accessible. A number of third-party maintenance utilities have permissions repair functions, but Apple's Disk Utility is the default tool for running a permissions repair. Launch it and select the boot drive, and then in the "First Aid" tab (the default tab) click the button to repair disk permissions.
If the problem is happening only with one application, then the help files associated with that application may either be corrupted or nonexistant because of an installation error. First try the permissions repair, but if that does not work then try reinstalling the application.
In rare instances, applications may be installed by one user in ways were help files and support documentation get installed to that user's library. In this case the files will not be available to other user accounts, and the program will either have to be installed or configured for that user or be fully reinstalled to be available for all users. Again, this is a rare occurrence, but is a possibility.