Sometimes when I try to open an application program I get an error message such as:

"The application <name> could not be opened because "<some>Lib" could not be found."

The file that the computer could not find always has "Lib" in its title. Is there some common thread to this kind of error message?

Yes. "Lib" is short for "Library." System software can be packaged as reusable libraries. The same libraries can be used by many different applications or control panels. For this reason, they are called "Shared Libraries." Shared Libraries are most commonly contained in pieces of the system software such as the System suitcase file, System Resources, Mac OS ROM or extensions.

Unfortunately, any of these can (and almost always do) contain many shared libraries. Therefore, the error messages referring to the missing library do not always refer to a specific file. However, the error message can still help you narrow down to a few files.

For example:

Suppose you try to open the File Sharing control panel and get a message about "OTUtilityLib" missing. If you know that "OT" is a common abbreviation for "Open Transport", the networking software for Mac OS (since System 7.5.2), then you would know to look for extensions with "Open Transport" in the title. This makes sense since the File Sharing control panel is for letting us share files over a network. Naturally, we need the networking software.

In this case, some of the required files also have names starting with "OpenTpt". Sometimes the abbreviation of file names makes this harder than it would otherwise be.

You can get these error messages if the file is disabled in the Extensions Manager control panel, missing from the hard drive altogether or damaged.

To turn on disabled extensions:

1. Open the Extensions Manager control panel.
   
2. Find extensions that seem like they might be related and turn them on.
   
3. Click the restart button and try again.

To reinstall missing or damaged extensions:

1. Run the system software installer for Mac OS or Apple Software Restore CD that came with your computer.
   
2. If you are running the Mac OS installer (but not an Apple Software Restore CD), then you can choose a customized package with just the component that you are trying to reinstall. This is the quickest way to resinstall a few things. This will not touch parts of your System Folder whose components you are not reinstalling.