Symptom
Using a Classic application, you cannot save files to certain write-protected Mac OS X directories (such as /System).
Solution
Save in a different location, such as the desktop, the Documents folder, or your home directory.
Before saving a document, make sure the target directory is not write-protected, such as /System. You can determine access (including write) permissions by selecting the directory in the Finder and choosing Finder > Get Info. Look in Ownership and Permissions for the directory's access privileges.